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Introduction to JavaScript

What is javascript .

JavaScript is a lightweight, cross-platform , single-threaded, and interpreted compiled programming language. It is also known as the scripting language for webpages. It is well-known for the development of web pages, and many non-browser environments also use it.

JavaScript is a weakly typed language (dynamically typed) . JavaScript can be used for Client-side developments as well as Server-side developments. JavaScript is both an imperative and declarative type of language. JavaScript contains a standard library of objects, like Array , Date , and Math , and a core set of language elements like operators , control structures , and statements .

Client-side: It supplies objects to control a browser and its Document Object Model (DOM). Like if client-side extensions allow an application to place elements on an HTML form and respond to user events such as mouse clicks , form input , and page navigation . Useful libraries for the client side are AngularJS , ReactJS , VueJS, and so many others.
Server-side: It supplies objects relevant to running JavaScript on a server. For if the server-side extensions allow an application to communicate with a database, and provide continuity of information from one invocation to another of the application, or perform file manipulations on a server. The useful framework which is the most famous these days is node.js .
Imperative language – In this type of language we are mostly concerned about how it is to be done. It simply controls the flow of computation. The procedural programming approach, object, oriented approach comes under this as async await we are thinking about what is to be done further after the async call.
Declarative programming – In this type of language we are concerned about how it is to be done, basically here logical computation requires. Her main goal is to describe the desired result without direct dictation on how to get it as the arrow function does.

How to Link JavaScript File in HTML ?

JavaScript can be added to HTML file in two ways :

Internal JS: We can add JavaScript directly to our HTML file by writing the code inside the <script> tag. The <script> tag can either be placed inside the <head> or the <body> tag according to the requirement.
External JS : We can write JavaScript code in another files having an extension.js and then link this file inside the <head> tag of the HTML file in which we want to add this code.

Output: The output will display on the console.

JavaScript Introduction

History of JavaScript

It was created by Brendan Eich in 1995. He was an engineer at Netscape. It was originally going to be named LiveScript but was renamed. Unlike most programming languages, JavaScript language has no concept of input or output. It is designed to run as a scripting language in a host environment, and it is up to the host environment to provide mechanisms for communicating with the outside world. The most common host environment is the browser.

Features of JavaScript

According to a recent survey conducted by Stack Overflow , JavaScript is the most popular language on earth. With advances in browser technology and JavaScript having moved into the server with Node.js and other frameworks, JavaScript is capable of so much more. Here are a few things that we can do with JavaScript:

JavaScript was created in the first place for DOM manipulation. Earlier websites were mostly static, after JS was created dynamic Web sites were made.
Functions in JS are objects. They may have properties and methods just like other objects. They can be passed as arguments in other functions.
Can handle date and time.
Performs Form Validation although the forms are created using HTML.
No compiler is needed.

Applications of JavaScript

Web Development : Adding interactivity and behavior to static sites JavaScript was invented to do this in 1995. By using AngularJS that can be achieved so easily.
Web Applications: With technology, browsers have improved to the extent that a language was required to create robust web applications. When we explore a map in Google Maps then we only need to click and drag the mouse. All detailed view is just a click away, and this is possible only because of JavaScript. It uses Application Programming Interfaces(APIs) that provide extra power to the code. The Electron and React are helpful in this department.
Server Applications: With the help of Node.js, JavaScript made its way from client to server and Node.js is the most powerful on the server side.
Games: Not only in websites, but JavaScript also helps in creating games for leisure. The combination of JavaScript and HTML 5 makes JavaScript popular in game development as well. It provides the EaseJS library which provides solutions for working with rich graphics.
Smartwatches: JavaScript is being used in all possible devices and applications. It provides a library PebbleJS which is used in smartwatch applications. This framework works for applications that require the Internet for their functioning.
Art: Artists and designers can create whatever they want using JavaScript to draw on HTML 5 canvas, and make the sound more effective also can be used p5.js library.
Machine Learning: This JavaScript ml5.js library can be used in web development by using machine learning.
Mobile Applications: JavaScript can also be used to build an application for non-web contexts. The features and uses of JavaScript make it a powerful tool for creating mobile applications. This is a Framework for building web and mobile apps using JavaScript. Using React Native, we can build mobile applications for different operating systems. We do not require to write code for different systems. Write once use it anywhere!

Limitations of JavaScript

Security risks: JavaScript can be used to fetch data using AJAX or by manipulating tags that load data such as <img>, <object>, <script>. These attacks are called cross-site script attacks. They inject JS that is not part of the site into the visitor’s browser thus fetching the details.
Performance: JavaScript does not provide the same level of performance as offered by many traditional languages as a complex program written in JavaScript would be comparatively slow. But as JavaScript is used to perform simple tasks in a browser, so performance is not considered a big restriction in its use.
Complexity: To master a scripting language, programmers must have a thorough knowledge of all the programming concepts, core language objects, and client and server-side objects otherwise it would be difficult for them to write advanced scripts using JavaScript.
Weak error handling and type checking facilities: It is a weakly typed language as there is no need to specify the data type of the variable. So wrong type checking is not performed by compile.

Why JavaScript is known as a lightweight programming language ?

JavaScript is considered lightweight due to the fact that it has low CPU usage, is easy to implement, and has a minimalist syntax. Minimalist syntax as in, has no data types. Everything is treated here as an object. It is very easy to learn because of its syntax similar to C++ and Java.

A lightweight language does not consume much of your CPU’s resources. It doesn’t put excess strain on your CPU or RAM. JavaScript runs in the browser even though it has complex paradigms and logic which means it uses fewer resources than other languages. For example, NodeJs, a variation of JavaScript not only performs faster computations but also uses fewer resources than its counterparts such as Dart or Java.

Additionally, when compared with other programming languages, it has fewer in-built libraries or frameworks, contributing as another reason for it being lightweight. However, this brings a drawback in that we need to incorporate external libraries and frameworks.

Is JavaScript Compiled or Interpreted or both ?

JavaScript is both compiled and interpreted. In the earlier versions of JavaScript, it used only the interpreter that executed code line by line and shows the result immediately. But with time the performance became an issue as interpretation is quite slow. Therefore, in the newer versions of JS, probably after the V8, the JIT compiler was also incorporated to optimize the execution and display the result more quickly. This JIT compiler generates a bytecode that is relatively easier to code. This bytecode is a set of highly optimized instructions. The V8 engine initially uses an interpreter, to interpret the code. On further executions, the V8 engine finds patterns such as frequently executed functions, and frequently used variables, and compiles them to improve performance.

JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples .

Introduction to JavaScript – FAQs

What is javascript.

JavaScript is a high-level, dynamic programming language used to make web pages interactive. It is a core technology of the World Wide Web, alongside HTML and CSS.

What is JavaScript used for ?

JavaScript is a versatile programming language primarily used for web development. It adds interactivity, dynamic content, and enhanced user experiences to websites. With JavaScript, you can create features like sliders, interactive forms, animations, and more. It’s also widely used in building web applications, backend services (using Node.js), game development, and even mobile apps.

What is the difference between JavaScript and Java?

JavaScript and Java are distinct languages with different purposes. Java is an object-oriented programming language for building standalone applications, while JavaScript is primarily used to enhance web pages with interactivity and dynamic content.

What is JavaScript DOM ?

The JavaScript DOM (Document Object Model) is a programming interface that allows you to interact with and manipulate HTML and CSS. The DOM represents the structure of a web page as a tree of objects that JavaScript can modify. You can use the DOM to update content, change styles, handle events, and interact with elements in real-time, making your web pages dynamic and responsive.

How do you include JavaScript in an HTML document?

JavaScript can be included in an HTML document in three ways: Inline, by placing it directly within HTML elements. Internal, by placing it within a <script> tag in the HTML document. External, by linking to a separate .js file using the <script src=”filename.js”></script> tag.

What are variables in JavaScript?

Variables in JavaScript store data values. They can be declared using var, let, or const.

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What is JavaScript? The full-stack programming language

Javascript is the most in-demand programming language for developer jobs and one of the most versatile languages for full-stack development. here's what you need to know about javascript..

shutterstock 1361674454 JavaScript Hello code in programming text editor

JavaScript is a wildly popular interpreted scripting language that was the most in-demand language of 2023 , with 29% of job offers requiring programming experience with JavaScript or TypeScript. There are various reasons for JavaScript’s success, starting from the fact that it’s an open standard, not controlled by any single vendor, with numerous implementations and a syntax that is easy to learn.

Just about anything interactive or animated on a webpage today is rendered in JavaScript. Thanks to server-side frameworks such as Node.js , Deno , and bun , the language also extends beyond the browser. It is used to write code for anything from clients to servers to cloud-based applications.

This is an overview of JavaScript, including a brief history, what kinds of applications it is used for, tools for working with JavaScript, and resources for learning JavaScript.

A brief history of JavaScript

As its name implies, JavaScript is a scripting language. Traditional languages such as C++ are compiled before they’re run into executable binary form, with the compiler checking for errors in the entire program before the process is complete. Scripting languages, by contrast, are executed one line at a time by another program called an interpreter. Scripting languages started out as a series of shell commands used to execute other programs. Their flexibility and ease of use made them a popular type of programming language in their own right, and languages like JavaScript became important with the rise of the web.

Many developers new to JavaScript wonder about the Java part of its name. The short story is that Java and JavaScript emerged during the same historic moment, and both were key to the birth of the web. Their history is intertwined, but the two languages are separate. Brendan Eich, JavaScript’s creator, explained why JavaScript was considered an important complement to Java in the original Netscape browser:

There were people who argued strongly that Java’s fine for programmers who build components, but there’s a much larger audience of people who write scripts or maybe copy a script from somebody else and tweak it. These people are less specialized and may be paid to do something other than programming, like administer a network, and they write scripts part-time or on the side. If they’re writing small pieces of code, they just want to get their code done with the minimal amount of fuss.

Originally called LiveScript, the language was created with syntax that was superficially similar to Java in order to tap into the emerging Java developer community. Even though its usage grew in tandem with Java and early web development, JavaScript was long considered a lesser sidekick to the more robust Java programming language.

In 1997, the ECMA (European Computer Manufacturers Association) issued a standard defining the language that anyone could implement. The reason for this move was that “Java” remained a Sun trademark that only Netscape had a license to use. The new, standardized version of JavaScript was dubbed ECMAScript , but in practice, most people know the language as JavaScript.

What is JavaScript used for?

JavaScript was developed to help create interactive websites, and this remains one of its primary uses today. Developers incorporate JavaScript into their website code, where it is executed by the interpreter built into the user’s browser. The JavaScript code creates or modifies HTML on the fly to produce dynamic content and interact with back-end data stores. When used this way, JavaScript is called a client-side language, with one of its most lucrative applications being mobile games. Server-side frameworks like Node.js extend JavaScript for more scalable and event-driven applications.

Advantages of using JavaScript

You won’t hear anyone arguing that JavaScript is a perfect language, but it is a very useful one. It’s easy to write workable code quickly in JavaScript, and while interpreted languages often don’t perform well compared to compiled code, JavaScript has a special advantage here because it was initially created for web browsers. Three of the biggest software companies in the world—Microsoft, Apple, and Google—compete to produce high-performance JavaScript interpreters. As a result, JavaScript is a remarkably robust and scalable language, even given its humble beginnings.

Once non-browser viable JavaScript runtimes became widely available, the army of web developers well-versed in JavaScript suddenly found themselves crowned as full-stack developers . The JavaScript tooling ecosystem boosts developer productivity with code that gets the job done from the browser to the server. Due to its popularity, the language is also frequently updated. It’s a classic example of a virtuous cycle of popularity driving adoption.

JavaScript libraries and frameworks

You’ll sometimes hear people refer to vanilla JavaScript . This, in a nutshell, means you’re working with an application that was written in JavaScript from the ground up. This is fine for small bits of functionality, but once you start working at scale, it quickly becomes untenable, as any enterprise developer will tell you. Most JavaScript developers make frequent use of the vast array of available JavaScript libraries —prewritten third-party code, usually free and open source, that solves a common problem and can be integrated into your project. (The ECMAScript standard refers to JavaScript modules , but library is the more commonly used term in practice.)

Most JavaScript developers turn to libraries for basic application plumbing rather than reinventing the wheel. There are also frameworks , which are collections of libraries designed to work together to provide the scaffolding for enterprise-scale applications. Using frameworks lets developers focus on the technical aspects of their programs. Probably the most famous JavaScript framework is Angular . Others include React and Vue .

TypeScript: A superset of JavaScript

An important aspect of the JavaScript ecosystem is TypeScript , which is similar to JavaScript but has features that the basic language lacks, like strong typing of variables and other data structures. TypeScript and languages like it are often designed to bring to JavaScript concepts that make it easier to build sprawling enterprise-scale applications efficiently; TypeScript in particular was created at Microsoft when the company was developing a web-based version of its flagship Office suite.

TypeScript is said to be a superset of JavaScript because its syntax includes everything in JavaScript, and then some : good JavaScript is always good TypeScript, but TypeScript has syntax that isn’t part of JavaScript. TypeScript code is transpiled into ordinary JavaScript, allowing it to run in browsers and on standard JavaScript runtimes. Learn more about the similarities and differences between TypeScript and JavaScript .

Resources for learning JavaScript

If you are serious about becoming a JavaScript developer you’ll want to go deeper than this article. The W3Schools JavaScript tutorial is great for your first dive into JavaScript syntax. Here are some additional articles and tutorials to help you get started:

The Modern JavaScript Tutorial is a comprehensive resource that takes you step by step from a simple Hello, World! program to ways to build sophisticated interactive functionality into the browser.
JavaScript Examples at Tutorial Republic offer a wealth of short JavaScript programs that escalate in difficulty so you can see how JavaScript code works in action.
InfoWorld’s Matthew Tyson writes frequently about JavaScript frameworks and programming techniques. Popular recent articles include Using JavaScript and forms , Using JavaScript’s built-in objects , and Building JavaScript tables in React .

JavaScript Snake is a live example of what you can do with JavaScript. It’s a classic game that can be built to run in the browser using only JavaScript, HTML, and CSS. This tutorial from Panayiotis Nicolaou shows you how.

Get started with JavaScript

Are you ready to start playing around with JavaScript today? Because it’s an interpreted language, you don’t need to download JavaScript. You can just fire up your favorite text editor (or better yet, a JavaScript editor or IDE) and start typing code! A JavaScript interpreter is built into any web browser that executes commands, so you can simply embed your JavaScript into an HTML document and load it up to test.

If you want to run JavaScript code in a desktop environment—which will give you access to the filesystem, among other things—then you can download Node.js .

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What is JavaScript?

Server-side versus client-side code

Inline javascript handlers.

Welcome to the MDN beginner's JavaScript course! In this first article we will look at JavaScript from a high level, answering questions such as "what is it?", and "what is it doing?", and making sure you are comfortable with JavaScript's purpose.

Prerequisites:	Basic computer literacy, a basic understanding of HTML and CSS.
Objective:	To gain familiarity with what JavaScript is, what it can do, and how it fits into a web site.

A high-level definition

JavaScript is a programming language that allows you to implement complex things on web pages — every time a web page does more than just sit there and display static information for you to look at — displaying timely content updates, or interactive maps, or animated 2D/3D graphics, or scrolling video jukeboxes, etc. — you can bet that JavaScript is probably involved. It is the third layer of the layer cake of standard web technologies, two of which ( HTML and CSS ) we have covered in much more detail in other parts of the Learning Area.

HTML is the markup language that we use to structure and give meaning to our web content, for example defining paragraphs, headings, and data tables, or embedding images and videos in the page.
CSS is a language of style rules that we use to apply styling to our HTML content, for example setting background colors and fonts, and laying out our content in multiple columns.
JavaScript is a programming language that enables you to create dynamically updating content, control multimedia, animate images, and pretty much everything else. (Okay, not everything, but it is amazing what you can achieve with a few lines of JavaScript code.)

The three layers build on top of one another nicely. Let's take a simple text label as an example. We can mark it up using HTML to give it structure and purpose:

Then we can add some CSS into the mix to get it looking nice:

And finally, we can add some JavaScript to implement dynamic behaviour:

Try clicking on the text label to see what happens (note also that you can find this demo on GitHub — see the source code , or run it live )!

JavaScript can do a lot more than that — let's explore what in more detail.

So what can it really do?

The core JavaScript language consists of some common programming features that allow you to do things like:

Store useful values inside variables. In the above example for instance, we ask for a new name to be entered then store that name in a variable called name .
Operations on pieces of text (known as "strings" in programming). In the above example we take the string "Player 1: " and join it to the name variable to create the complete text label, e.g. ''Player 1: Chris".
Running code in response to certain events occurring on a web page. We used a click event in our example above to detect when the button is clicked and then run the code that updates the text label.)
And much more!

What is even more exciting however is the functionality built on top of the core JavaScript language. So-called Application Programming Interfaces ( APIs ) provide you with extra superpowers to use in your JavaScript code.

APIs are ready-made sets of code building blocks that allow a developer to implement programs that would otherwise be hard or impossible to implement. They do the same thing for programming that ready-made furniture kits do for home building — it is much easier to take ready-cut panels and screw them together to make a bookshelf than it is to work out the design yourself, go and find the correct wood, cut all the panels to the right size and shape, find the correct-sized screws, and then put them together to make a bookshelf.

They generally fall into two categories.

Browser APIs are built into your web browser, and are able to expose data from the surrounding computer environment, or do useful complex things. For example:

The DOM (Document Object Model) API allows you to manipulate HTML and CSS, creating, removing and changing HTML, dynamically applying new styles to your page, etc. Everytime you see a popup window appear on a page, or some new content displayed (as we saw above in our simple demo) for example, that's the DOM in action.
The Geolocation API retrieves geographical information. This is how Google Maps is able to find your location, and plot it on a map.
The Canvas and WebGL APIs allow you to create animated 2D and 3D graphics. People are doing some amazing things using these web technologies —see Chrome Experiments and webglsamples .
Audio and Video APIs like HTMLMediaElement and WebRTC allow you to do really interesting things with multimedia, such as play audio and video right in a web page, or grab video from your web camera and display it on someone else's computer (try our simple Snapshot demo to get the idea).

Note : Many of the above demos won't work in a older browser — when experimenting, it's a good idea to use a modern browser like Firefox, Chrome, Edge or Opera to run your code in. You will need to consider cross browser testing in more detail when you get closer to delivering production code (i.e. real code that real customers will use).

Third party APIs are not built into the browser by default, and you generally have to grab their code and information from somewhere on the Web. For example:

The Twitter API allows you to do things like displaying your latest tweets on your website.
The Google Maps API allows you to embed custom maps into your website, and other such functionality.

Note : These APIs are advanced, and we'll not be covering any of these in this module. You can find out much more about these in our Client-side web APIs module .

There's a lot more available, too! However, don't get over excited just yet. You won't be able to build the next Facebook, Google Maps or Instagram after studying JavaScript for 24 hours — there's a lot of basics to cover first. And that's why you're here — let's move on!

What is JavaScript doing on your page?

Here we'll start actually looking at some code, and while doing so explore what actually happens when you run some JavaScript in your page.

Let's briefly recap the story of what happens when you load a web page in a browser (first talked about in our How CSS works article). When you load a web page in your browser, you are running your code (the HTML, CSS, and JavaScript) inside an execution environment (the browser tab). This is like a factory that takes in raw materials (the code) and outputs a product (the web page).

The JavaScript is executed by the browser's JavaScript engine, after the HTML and CSS have been assembled and put together into a web page. This ensures that the structure and style of the page are already in place by the time the JavaScript starts to run.

This is a good thing, as a very common use of JavaScript is to dynamically modify HTML and CSS to update a user interface, via the Document Object Model API (as mentioned above). If the JavaScript loaded and tried to run before the HTML and CSS was there to affect, then errors would occur.

Browser security

Each browser tab is its own separate bucket for running code in (these buckets are called "execution environments" in technical terms) — this means that in most cases the code in each tab is run completely separately, and the code in one tab cannot directly affect the code in another tab — or on another website. This is a good security measure — if this were not the case, then pirates could start writing code to steal information from other websites, and other such bad things.

Note : There are ways to send code and data between different websites/tabs in a safe manner, but these are advanced techniques that we won't cover in this course.

JavaScript running order

When the browser encounters a block of JavaScript, it generally runs it in order, from top to bottom. This means that you need to be careful what order you put things in. For example, let's return to the block of JavaScript we saw in our first example:

Here we are selecting a text paragraph (line 1), then attaching an event listener to it (line 3) so that when the paragraph is clicked, the updateName() code block (lines 5–8) is run. The updateName() code block (these types of reusable code block are called "functions") asks the user for a new name, and then inserts that name into the paragraph to update the display.

If you swapped the order of the first two lines of code, it would no longer work — instead, you'd get an error returned in the browser developer console — TypeError: para is undefined . This means that the para object does not exist yet, so we can't add an event listener to it.

Note : This is a very common error — you need to be careful that the objects referenced in your code exist before you try to do stuff to them.

Interpreted versus compiled code

You might hear the terms interpreted and compiled in the context of programming. JavaScript is an interpreted language — the code is run from top to bottom and the result of running the code is immediately returned. You don't have to transform the code into a different form before the browser runs it.

Compiled languages on the other hand are transformed (compiled) into another form before they are run by the computer. For example C/C++ are compiled into assembly language that is then run by the computer.

Both approaches have different advantages, which we won't discuss at this point.

You might also hear the terms server-side and client-side code, specially in the context of web development. Client-side code is code that is run on the user's computer — when a web page is viewed, the page's client-side code is downloaded, then run and displayed by the browser. In this JavaScript module we are explicitly talking about client-side JavaScript .

Server-side code on the other hand is run on the server, then its results are downloaded and displayed in the browser. Examples of popular server-side web languages include PHP, Python, Ruby, and ASP.NET. And JavaScript! JavaScript can also be used as a server-side language, for example in the popular Node.js environment — you can find more out about server-side JavaScript in our Dynamic Websites – Server-side programming topic.

The word dynamic is used to describe both client-side JavaScript, and server-side languages — it refers to the ability to update the display of a web page/app to show different things in different circumstances, generating new content as required. Server-side code dynamically generates new content on the server, e.g. pulling data from a database, whereas client-side JavaScript dynamically generates new content inside the browser on the client, e.g. creating a new HTML table, inserting data requested from the server into it, then displaying the table in a web page shown to the user. The meaning is slightly different in the two contexts, but related, and both approaches (server-side and client-side) usually work together.

A web page with no dynamically updating content is referred to as static — it just shows the same content all the time.

How do you add JavaScript to your page?

JavaScript is applied to your HTML page in a similar manner to CSS. Whereas CSS uses element specifies relationships between the current document and an external resource. Possible uses for this element include defining a relational framework for navigation. This element is most used to link to style sheets."> <link> elements to apply external stylesheets and element contains style information for a document, or part of a document. By default, the style instructions written inside that element are expected to be CSS."> <style> elements to apply internal stylesheets to HTML, JavaScript only needs one friend in the world of HTML — the element is used to embed or reference an executable script."> <script> element. Let's learn how this works.

Internal JavaScript

First of all, make a local copy of our example file apply-javascript.html . Save it in a directory somewhere sensible.
Open the file in your web browser and in your text editor. You'll see that the HTML creates a simple web page containing a clickable button.
Next, go to your text editor and add the following just before your closing </body> tag: <script> // JavaScript goes here </script>
Now we'll add some JavaScript inside our element is used to embed or reference an executable script."> <script> element to make the page do something more interesting — add the following code just below the "// JavaScript goes here" line: function createParagraph() { var para = document.createElement('p'); para.textContent = 'You clicked the button!'; document.body.appendChild(para); } var buttons = document.querySelectorAll('button'); for (var i = 0; i < buttons.length ; i++) { buttons[i].addEventListener('click', createParagraph); }
Save your file and refresh the browser — now you should see that when you click the button, a new paragraph is generated and placed below.

Note : If your example doesn't seem to work, go through the steps again and check that you did everything right. Did you save your local copy of the starting code as a .html file? Did you add your element is used to embed or reference an executable script."> <script> element just before the </body> tag? Did you enter the JavaScript exactly as shown? JavaScript is case sensitive, and very fussy, so you need to enter the syntax exactly as shown, otherwise it may not work.

Note : You can see this version on GitHub as apply-javascript-internal.html ( see it live too ).

External JavaScript

This works great, but what if we wanted to put our JavaScript in an external file? Let's explore this now.

First, create a new file in the same directory as your sample HTML file. Call it script.js — make sure it has that .js filename extension, as that's how it is recognized as JavaScript.
Next, copy all of the script out of your current element is used to embed or reference an executable script."> <script> element and paste it into the .js file. Save that file.
Now replace your current element is used to embed or reference an executable script."> <script> element with the following: <script src="script.js"></script>
Save and refresh your browser, and you should see the same thing! It works just the same, but now we've got the JavaScript in an external file. This is generally a good thing in terms of organizing your code, and making it reusable across multiple HTML files. Plus the HTML is easier to read without huge chunks of script dumped in it.

Note : You can see this version on GitHub as apply-javascript-external.html and script.js ( see it live too ).

Note that sometimes you'll come across bits of actual JavaScript code living inside HTML. It might look something like this:

You can try this version of our demo below.

This demo has exactly the same functionality as in the previous two sections, except that the element represents a clickable button."> <button> element includes an inline onclick handler to make the function run when the button is pressed.

Please don't do this, however. It is bad practice to pollute your HTML with JavaScript, and it is inefficient — you'd have to include the onclick="createParagraph()" attribute on every button you wanted the JavaScript to apply to.

Using a pure JavaScript construct allows you to select all the buttons using one instruction. The code we used above to serve this purpose looks like this:

This might look a bit longer than the onclick attribute, but this will work for all buttons no matter how many are on the page, and how many are added or removed. The JavaScript does not need to be changed.

Note : Try editing your version of apply-javascript.html and add a few more buttons into the file. When you reload, you should find that all of the buttons when clicked will create a paragraph. Neat, huh?

As with HTML and CSS, it is possible to write comments into your JavaScript code that will be ignored by the browser, and exist simply to provide instructions to your fellow developers on how the code works (and you, if you come back to your code after 6 months and can't remember what you did). Comments are very useful, and you should use them often, particularly for larger applications. There are two types:

A single line comment is written after a double forward slash (//), e.g. // I am a comment
A multi-line comment is written between the strings /* and */, e.g. /* I am also a comment */

So for example, we could annotate our last demo's JavaScript with comments like so:

So there you go, your first step into the world of JavaScript. We've begun with just theory, to start getting you used to why you'd use JavaScript, and what kind of things you can do with it. Along the way you saw a few code examples and learned how JavaScript fits in with the rest of the code on your website, amongst other things.

JavaScript may seem a bit daunting right now, but don't worry — in this course we will take you through it in simple steps that will make sense going forward. In the next article we will plunge straight into the practical , getting you to jump straight in and build your own JavaScript examples.

In this module

A first splash into JavaScript
What went wrong? Troubleshooting JavaScript
Storing the information you need — Variables
Basic math in JavaScript — numbers and operators
Handling text — strings in JavaScript
Useful string methods
Assessment: Silly story generator

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A detailed guide on JavaScript Web Development

By Mohit Joshi, Community Contributor - August 7, 2023

The most widely used programming language in the world, JavaScript has enriched the whole digital realm by enabling developers to build dynamic websites with visually appealing user interfaces . Web Developers that are just starting or seasoned pro developers, everyone is playing with JavaScript, a fundamental route for building successful web applications .

If you’ve lived through the early decade of the century or the pre-JavaScript era, you must have wondered how far things have come across. The websites back then were not only less pleasant but were not even handy. So you might claim that JavaScript does more than just give your websites a pretty face; it also improves their usability and accessibility . If it’s difficult for you to imagine a world without JavaScript, you may just disable JavaScript in your browser and see how you can’t endure the lifeless web pages for more than a few minutes.

In this guide, we are diving into the fundamental understanding of how to leverage JavaScript for web development .

StackOverflow

What is JavaScript for Web Development?

Different types of web development, top javascript frameworks for web development, getting started with javascript for web development: with example, 1. variables, 2. operators, 3. functions, 4. conditional statements, best practices for using javascript web development.

JavaScript is a high-level interpreted programming language that was initially launched in 1995 but came into wider public usage much later. It is an engine that is used for building interactive aspects in the websites that broadens the functionality .

If you come across components in any websites, that utilize animations, maps, graphics, etc., you can be confident that JavaScript is behind all those functionalities. It is a lightweight and object-oriented programming language that is being used by the majority of modern websites available on the internet. It is cross-platform compatible and is supported by all major web browsers.

Both the front end and the back end of websites may be developed using JavaScript, which, when done right, captures seamless communication between the client and the server. The potential of JavaScript to manipulate the DOM is its main benefit for use in modern web development.

Also Read: Understanding JavaScript design patterns in depth

Why is JavaScript Important for Web Development?

It is hard to imagine developing user-friendly websites without dealing with JavaScript. It not only makes the entire development process easier, but it also adds features you wouldn’t get from any other technology. Let’s look at the three top-most important criteria for using JavaScript for web development.

Cross-platform compatibility : JavaScript is supported on almost all modern web browsers present across the world. This has accepted JavaScript as one of the most essential and widely used client-side scripting languages. It not only ensures a seamless experience as a user but also ensures broader coverage of your website as a developer.
Community Support: Being among the most popular programming languages in the world, JavaScript also ensures a vast collection of resources, tools, documentation, and community support. As a developer, you can go through numerous active forums, tutorials, and open-source projects due to their wide acceptance as a programming language among web developers throughout the world.
Client and Server side capabilities: JavaScript is well-known for building client-side webpages, enhancing the website’s user-friendliness, and adding cutting-edge interactive features. However, as the modern world evolved, JavaScript also expanded its capabilities of scripting the server side of the website with the help of NodeJS.

Also Read: How to test JavaScript in browsers

Typically, there are two steps involved in creating a website: front-end development and back-end development. In most cases, each part is developed by separate developers with different skill sets, however, When a single developer oversees the entire development of the website, they are known as full-stack developers. Let’s understand both parts of the development and what are their essential features.

Front-end development: It is also known as client-side development, as the name suggests it focuses on the visible parts of the websites that are UI components of an application. This development assures the website is responsive , user-friendly, stylish, and visually appealing in all aspects.
Back-end development: It is also known as server-side development, as it ensures the logic is properly applied on the website as intended by the developer. The developer here creates a behind-the-scene show that powers the website creates a connection of the front end of the website with the required servers and databases, and ensures a seamless transaction of data between them.

Read More: Front End Testing: A Beginner’s Guide

A large ecosystem of frameworks and libraries that use JavaScript and provide several modern features and enhancements essential for web development exists. Since all the frameworks we’re going to talk about are built on JavaScript, learning them won’t take much time if you know JavaScript well.

Let’s look at the top frameworks based on JavaScript for web development.

NodeJS: NodeJS expands the capabilities of JavaScript, enabling programmers to build whole applications using only JavaScript. It allows to build a strong back end for any web application without having to learn any new programming language and leveraging JavaScript itself.
ReactJS: It is an open-source UI development JavaScript library for developing the front end of websites. A ReactJS website is a collection of several reusable components, each being a building block of the website. The implementation of reusable components using JavaScript has reduced the development time and complexity of development.

Read More: React Testing: How to test React components?

VueJS: VueJS is an open-source front-end framework used for creating dynamic user-interface and single-page applications (SPAs). Vue.Js enables developers to write code in JSX. However, the components are created in HTML components, therefore, allowing even beginner developers an easy-learning curve.
AngularJS: Angular is an open-source full-fledged web application framework based on TypeScript used for creating single-page applications (SPAs). As soon as it was launched, it caught several eyes, due to its excellent features. Moreover, AngularJS gained the enormous trust of developers because it is backed by a tech giant, Google.

Also Read: Angular vs React vs Vue: Core differences

You don’t need to rely on any third-party services while using JavaScript for Web Development, and you don’t even need to install a lot of packages in order to start writing JavaScript code.

Prerequisite:

Install any IDE of your choice. In this example, we are using VS code as our code editor.

JavaScript Basics for Web Development

To begin with, JavaScript, just like we add CSS, we shall add the following code before the closing body tag in the HTML file to link the JavaScript file.

Note that, our JavaScript file name is “script.js” .

To make sure it works, insert the following line of code in your JavaScript file and view the output in the browser. The alert “hello world” will pop out.

Variables are containers of data that can be used to store data of different types such as numbers, strings, objects, and more. To define a variable you may use, ‘var’ , ’let’ , and ‘const’ keywords. Variables can be used anytime in a document when once define. Let’s understand with an example.

And the output goes as.

You can use JavaScript as a calculator. You can expect JavaScript to support all the basic arithmetic operators. These operators are used wildly in websites for several purposes. Let’s understand what I’m saying with an example.

Functions are reusable blocks of code that are assigned some name to use anywhere throughout the document. Let’s create a function that when given two numbers, returns the output as the sum of those numbers.

In a JavaScript file, every code is executed line by line, however, if in some instances, we wish that some code should only be executed under some conditions, otherwise skip the script. This can be achieved by applying conditions in our code with the help of ‘if..else’.

Let’s understand this with the help of an example.

Conditional Statements in JavaScript Web Development

JavaScript objects are simply key-value pairs or data containers that contain properties and methods. Let’s understand JavaScript objects with the help of an example.

These were some of the fundamental concepts of JavaScript. Now, let’s unleash the full potential of JavaScript with its most essential feature, which is manipulating DOM.

Selecting HTML elements and adding an event listener

This part will show us how to really manipulate the DOM using JavaScript. To demonstrate that with an example whenever a button on the website is clicked, an alert is generated. This further demonstrates JavaScript’s dynamic nature.

Create a button in your HTML file.

Creating Button Element in JavaScript Web Development

First, you have to get the button to operate any related action to it. To do so, there are several methods such as.

getElementById()
getElementByClass()
getElementByName()
getElementByTagName()
querySelector()

Further when the HTML element is selected you may use the event listener function to it so it records the event that occurred. For example, if the button is clicked the event listener will record that the button is being clicked.

Let’s create a JavaScript code that creates an alert when the button is clicked.

Adding Event Listener to an Element in JavaScript Web Development

Now that we have come along so far, we have understood the capabilities of JavaScript, and how it has enhanced modern web development. Let’s now understand how to leverage JavaScript, so that we don’t lag in creating appealing websites. Here are some best practices you must follow to leverage JavaScript for web development.

Constant code style: To maximize efficiency when working on a large JavaScript project that involves developer collaboration, you must ensure that a code pattern and style have been mutually agreed upon. A consistent coding approach makes your code easier to read and prevents misunderstandings with other team members.
Use proper testing strategies: The process of testing determines if the output product works as intended. If you follow the right testing procedures, your code becomes less susceptible to risks and doesn’t malfunction. Common JavaScript testing techniques include things like avoiding using mock, utilizing try..catch, adopting the BDD approach, and more.
Keep up with the latest trends: If you stay up to date with the rapid speed of modern web development, you may actively contribute to the creation of user-friendly websites.
Proper Variable nomenclature: You must choose descriptive and meaningful names for variables, functions, and classes. This reduces misunderstanding among the project’s other participants and improves the readability of the code.

A website that engages well with the users stands out among the crowd. In this tutorial, we delved into a detailed discussion of using JavaScript for web development. JavaScript is the most popular and widely-used programming language across the globe. JavaScript has been able to completely change how websites are developed nowadays.

This article also discussed a number of JavaScript-based frameworks that have altered the development environment by introducing features and tools that lessen the complexity and duration of development while enhancing output. You also got an understanding of different JavaScript code practices that will enable our website to reach a wider audience and work flawlessly in all popular operating systems and browsers.

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Introduction to JavaScript

Despite its name, JavaScript is only related to Java in that the two share a few syntactic similarities. JavaScript's syntax in its initial development was loosely inspired by Java's syntax and it was called "LiveScript" when it first shipped in a beta version of Netscape Navigator in 1995, both to align with some of Netscape's other named offerings and as a nod to the fact that it runs "live" in the browser. Microsoft released their own implementation of JavaScript, "JScript," shortly afterwards with Internet Explorer 3.0.

Netscape submitted this early work to Ecma International , an organization that develops and publishes technical standards, to formalize and detail how this scripting language should be understood by other browsers. In 1997, Ecma International released ECMA-262, standardizing the first version of a scripting language called ECMAScript. ECMAScript is the standard that informs the creation of more specific scripting languages, for example, Microsoft's later work on the now-defunct JScript, Adobe's ActionScript, and JavaScript itself.

This distinction is important when discussing specific aspects and features of JavaScript. "ES5" refers to the first major "versioned" release of the ECMAScript standard in 2009, following years of more piecemeal development. "ES6" (or "ES2015") is shorthand for the standards set by the sixth edition of ECMAScript, released in 2015. After ES6, new editions of the ECMAScript standard have been released yearly, with each edition's changes and additions referred to by year as in "ES2016" or "ES2017".

The basic rules

Unlike compiled languages, JavaScript isn't translated from code a person writes into a form the browser can understand. A script is sent to the browser alongside assets like markup, images, and stylesheets, the browser interprets it the same way it was written: as a human-readable sequence of Unicode characters, parsed from left to right and top to bottom.

When a JavaScript interpreter receives a script, it first performs lexical analysis , parsing the long string of characters that makes up a script and converting it into the following discrete input elements:

Format control characters
Line terminators
Whitespace (almost always meaning tabs and spaces).

The results of a script won't persist after reloading or navigating away from the current page, unless you include explicit instructions to do otherwise in the script.

At a high level, JavaScript applications are made up of statements and expressions .

A statement is a unit of instruction made up of one or more lines of code that represent an action. For example, you can use the following statement to assign a value to a variable named myVariable :

To be interpreted correctly, statements must end in a semicolon. However, these semicolons aren't always required when writing JavaScript. A feature called automatic semicolon insertion lets a line break following a complete statement be treated as a semicolon if a missing semicolon would cause an error.

ASI is error correction, not a permissive aspect of JavaScript itself. Because relying too much on this error correction can lead to ambiguity that breaks your code, you should still manually end every statement with a semicolon.

Block statements

A block statement groups any number of statements and declarations inside a pair of braces ( {} ). It lets you combine statements in places where JavaScript expects only one.

You'll most frequently see block statements alongside control flow statements, such as if :

Expressions

An expression is a unit of code that results in a value, and can therefore be used wherever a value is expected. 2 + 2 is an expression that results in the value 4 :

The "grouping operator", a matched pair of enclosing parentheses, is used to group parts of an expression to ensure that a portion of the expression is evaluated as a single unit. For example, you might use a grouping operator to override the mathematical order of operations , or to improve the readability of code:

Weak typing

JavaScript is a weakly typed language, which means a data value doesn't need to be explicitly marked as a specific data type . Unlike a strongly typed language, JavaScript can infer the intended type from a value's context and convert the value to that type. This process is called type coercion .

For example, if you add a number to a string value in a strongly typed language, such as Python, the result is an error:

Instead of returning an error, JavaScript coerces the number value to a string and concatenates the two values, the most likely intended behavior when adding any value to a string:

Data types can also be explicitly coerced. The following example coerces the numeric value 100 to a string value of "100" using JavaScript's built-in toString method:

Case sensitivity

Unlike HTML and the majority of CSS, JavaScript itself is fully case sensitive. This means you must always capitalize everything consistently, from the properties and methods built into the language to the identifiers you define yourself.

JavaScript is whitespace insensitive. This means the interpreter ignores the amount and type (tabs or spaces) of whitespace used.

However, the presence of whitespace can be significant as a separator between lexical tokens:

[ tokens : [let] [x] ]

[ tokens : [letx] ]

Where whitespace is used to separate meaningful lexical tokens, the parser ignores the amount and type of whitespace:

[ tokens : [let] [x] [=] [2] ]

The same is true of line breaks, though there are cases where line breaks can cause issues by prematurely ending a statement ):

Stylistically speaking, some types of statement frequently occupy a single line:

While some statements commonly use multiple lines:

These conventions are strictly for the sake of readability, however. JavaScript interprets the previous examples in the same way as the following:

Because of this, an automated process that strips nonessential whitespace from script files to reduce transfer size is a common step in preparing JavaScript for a production environment, alongside a number of other optimizations.

Use of whitespace characters in JavaScript is largely a matter of author and maintainer preferences. JavaScript projects with multiple developers contributing code often suggest or enforce certain whitespace conventions to ensure consistent code formatting—for example, use of tabs or spaces to indent nested statements:

Check your understanding

What is an expression?

JavaScript is case sensitive.

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License , and code samples are licensed under the Apache 2.0 License . For details, see the Google Developers Site Policies . Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2024-03-31 UTC.

Should You Learn JavaScript? Advice for Newbie Web Developers

If you want to become a web developer, you’ll be wondering what programming languages to learn. Do you start with the easiest ones ? Or the most useful ones? Both?

With so many options these days, why learn JavaScript?

You’ve no doubt heard that it’s an important web technology, but perhaps you’re not sure if JavaScript is all that relevant these days. With so many frameworks out there providing ready-to-use code, is it really necessary to learn JavaScript from scratch ?

In this guide, we’ll explore what JavaScript does and whether or not it’s still useful. We’ll then look at some of the main reasons for learning the language, and consider why it’s necessary to learn plain JavaScript first, before libraries and frameworks.

If you’d like to jump into it, get started learning JavaScript with our free coding short course .

If you want to skip ahead to a certain section, just use the clickable menu below:

What is JavaScript and what does it do?
Is it still worth learning JavaScript in 2024?
Why learn JavaScript?
Why learn vanilla JavaScript first?
What’s the best way to learn JavaScript?

So—should you learn JavaScript? Let’s find out.

1. What is JavaScript and what does it do?

Before you start learning something new, it’s important to understand exactly what it is and what it does. This is especially useful when it comes to mastering a new programming language.

In simple terms, JavaScript is a programming language used to make websites interactive. If you think about the basic makeup of a website, you have HTML, which describes and defines the basic content and structure of the website, then you have CSS, which tells the browser how this HTML content should be displayed—determining things like color and font.

With just HTML and CSS, you have a website that looks good but doesn’t actually do much. JavaScript brings the website to life by adding functionality. It’s is responsible for elements that the user can interact with, such as drop-down menus, modal windows, and contact forms. It is also used to create things like animations, video players, and interactive maps.

Nowadays, JavaScript is an all-purpose programming language—meaning it runs across the entire software stack. The most popular application of it is on the client side (aka frontend), but since Node.js came on the scene , many people run JavaScript on the server side (aka backend) as well.

When used on the client side, JavaScript code is read, interpreted, and executed in the user’s web browser. When used on the server side, it is run on a remote computer. You can learn more about the difference between frontend and backend programming in our guide .

JavaScript isn’t only used to create websites. It can also be used to build browser-based games and, with the help of certain frameworks, mobile apps for different operating systems. The creation of new libraries and frameworks is also making it possible to build backend programs with the language, such as web apps and server apps.

If you’re interested in learning more, we’ve covered more examples of what is JavaScript used for , including code in more depth elsewhere. But now that we know some of the array of uses of this twenty five year-old language, why learn JavaScript right now?

2. Is it still worth learning JavaScript in 2024?

The world of web development is constantly moving. With so many new tools popping up all the time, not to mention the proliferation of generative AI and the programming tools that come with it it can be extremely difficult to know where you should focus your efforts.

As an aspiring developer, you’ll want to make sure that what you’re learning is still relevant in today’s industry.

If you’re having doubts about this language, don’t. It’s important to note that since its creation in 1995 JavaScript is pretty much everywhere on the web—and that’s not likely to change any time soon. According to the 2023 StackOverflow developer survey , it’s the most commonly used programming language for the 11th year in a row .

A glance at the PYPL index and the Tiobe Index show that JavaScript is right up there in terms of popularity and searches by coders.

It’s currently used by 94.5% of all websites and, despite originally being designed as a client-side language, JavaScript has now made its way to the server-side of websites (thanks to Node.js), mobile devices (thanks to React Native and Ionic) and desktop (courtesy of Electron). Package managers like npm make it even more powerful.

As long as people are interacting with the web, you can assume that JS is highly relevant—there’s no doubt that this is a language worth knowing! With that in mind, let’s look at some of the key benefits of becoming a JavaScript expert.

3. Why learn JavaScript?

The most obvious reason for learning JavaScript is if you have hopes of becoming a web developer.

Even if you haven’t got your heart set on a tech career, being proficient in this language will enable you to build websites from scratch—a pretty useful skill to have in today’s job market!

If you do want to become a web developer, here are some of the main reasons why you should learn JavaScript:

JavaScript experts are versatile

JavaScript is an extremely versatile language. Once you’ve mastered it, the possibilities are endless: you can code on the client-side (frontend) using Angular and on the server-side (backend) using Node.js.

You can also develop web, mobile, and desktop apps using React.js , React Native, and Electron, and you can even get involved in machine learning.

If you want to become a frontend developer , JavaScript is a prerequisite. However, that’s not the only career path open to you as a JS expert. Mastering this key programming language could see you go on to work in full-stack development, games development, information security software engineering, machine learning, and artificial intelligence—to name just a few!

Ultimately, if you want any kind of development or engineering career, proficiency in this language is almost a must. So the next step is to check out the range of JavaScript bootcamps out there and find the one which is best suited to your needs!

JavaScript experts are in-demand (and well-paid)

JavaScript is the most popular programming language in the world, so it’s no wonder that it’s one of the most sought-after skills in the web development industry today.

According to the Devskiller IT Skills and Hiring Report 2020 , 72% of companies are looking to hire JavaScript experts. Enter the search term “JavaScript” on job site Indeed and you’ll find over 81,000 jobs requiring this skill (in the US). Run the same search on LinkedIn and the results are in excess of 110,000.

At the same time, the global demand for the language seems to outweigh the expertise available on the market. According to this HackerRank report for 2023 , JavaScript is the fifth-most popular language that companies look for in a web developer, four times more than its nearest competitor, Bash.

The growing popularity of TypeScript also helps the popularity of JavaScript remain steady, as TypeScript is built on top of it.

Not only are JavaScript experts in demand—they are also well-paid. In the United States, JavaScript developers earn an average yearly base salary of $103,590 per year . We’ve covered this topic in more detail in our JavaScript salary guide , but as you can see, learning this language can really boost your earning potential as a developer.

JavaScript is beginner-friendly

Compared to many other programming languages, JavaScript offers one of the more beginner-friendly entry points into the world of coding.

The great thing about it is that it comes installed on every modern web browser —there’s no need to set up any kind of development environment, which means you can start coding with JavaScript right away!

Another advantage of learning JavaScript as your first programming language is that you get instant feedback; with a minimal amount of code, you’ll immediately see visible results. There’s also a huge JS community on sites like Stack Overflow , so you’ll find plenty of support as you learn.

Not only is it beginner-friendly; it will also set you up with some extremely valuable transferable skills.

JavaScript supports object-oriented, functional, and imperative styles of programming—skills which can be transferred to any new language you might learn later on, such as Python, Java, or C++.

The language provides a crucial introduction to key principles and practices that you’ll take with you throughout your career as a developer.

4. Why learn vanilla JavaScript first?

When deciding whether or not to learn this language, what you’re really asking is whether or not you should learn “vanilla” JavaScript.

Vanilla JavaScript just means the basic language without any libraries or frameworks. Let’s explore what this means in more detail now.

What is meant by vanilla JavaScript, libraries, and frameworks?

If you research the term “vanilla JavaScript”, you might run into some confusion; however, all you need to know is that vanilla JavaScript is used to refer to the native, standards-based, non-extended version.

There’s no difference between vanilla JavaScript and JavaScript—it’s just there to emphasize the usage of plain JavaScript without the use of libraries and frameworks.

So what are libraries and frameworks?

JavaScript libraries and frameworks both contain sets of prewritten, ready-to-use code—but they’re not the same thing.

You can think of a framework as your blueprint for building a website: it gives you a structure to work from, and contains ready-made components and tools that help you to build certain elements much quicker than if you were to code them from scratch. Some popular JavaScript frameworks include Angular, Ember, and Vue.

Read more: 8 of the Best JavaScript Frameworks for Beginners

Frameworks also contain libraries. Libraries are smaller than frameworks, and tend to be used for more specific cases. A JavaScript library contains sets of code which can be called upon to implement certain functions and features.

Let’s imagine you want to code a particular element into your website. You could write, say, ten lines of JavaScript from scratch—or you could take the condensed, ready-made version from your chosen library. Some examples of JavaScript libraries include jQuery , Lodash , and Underscore .

The easiest way to understand how frameworks and libraries work together is to imagine you are building a house. The framework provides the foundation and the structure, while the library enables you to add in ready-made components (like furniture) rather than building your own from scratch.

You can learn more about the relationship between languages and libraries in this post explaining the main differences between JavaScript and jQuery . For now, let’s go back to our original question: How important is it to learn vanilla JavaScript?

Should you learn vanilla JavaScript first?

When it comes to learning the language, it can be tempting to skip ahead to those time-saving frameworks and libraries we just talked about—and many developers do. However, there are many compelling arguments for learning plain JavaScript first.

While JavaScript frameworks may help you get the job done quicker, there’s only so far you can go if you don’t understand the core concepts behind these frameworks. Frontend developer Abhishek Nagekar describes how not learning vanilla JavaScript came back to bite him when he started learning the JavaScript frameworks Node and Express:

“As I went to write more and more code in Node and Express, I began to get stuck at even the tiniest problems. Suddenly, I was surrounded with words like callbacks, closures, event loop and prototype. It felt like I got a reintroduction to JavaScript, but this time, it was not a toddler playing in its cradle, it was something of a mysterious monster, challenging me on every other step for not having taken it seriously.”

If you want to become a developer who can innovate, not just execute, you need to understand the underlying principles of the web—not just the shortcuts. This means learning vanilla JavaScript before you move on to frameworks. In fact, understanding plain JavaScript will help you later on when it comes to deciding whether to use a framework for a certain project, and if so, which framework to use.

Ultimately, if you want to work as a web developer , it’s inevitable that you’ll encounter this web development language at almost every turn. Learning plain JavaScript first will make you a versatile engineer who can work on both the frontend and the backend, and it’ll equip you to solve complex problems independently—a key skill in the industry.

5. What is the best way to start learning JavaScript?

So: if you want to become any kind of web developer, you absolutely need to learn this language—and you should start with plain old vanilla JavaScript first.

If you’re to work out how long to give to get up to speed on the language, senior developer Marven shows you how long it should take to pick up JavaScript .

The best way to start learning JavaScript is to get hands-on. Once you’ve read up on what the language is and how it works, give it a go in your browser. If you’re using Google Chrome, just click “View” then select “Developer” from the drop-down menu. From there, select “JavaScript Console” and you’re good to go!

As with most things, there are plenty of good resources on the web for teaching yourself JavaScript. However, if you want a more structured approach, consider a mentored web development course .

Whichever route you take, make sure you spend enough time learning all the basics. Once you know JavaScript inside out, you’re well-equipped to tackle the more complex languages of the web, as well as to show the benefits to the next person who asks themselves why learn JavaScript when there are other coding options out there.

Should I Learn JavaScript?

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If you’re thinking about getting into software development or want to add coding to your resume, the choices are endless. Even a quick search on the best coding languages to learn will turn up multiple answers, making it difficult to know where to begin . We know the feeling. Everyone starts as a beginner, and it can be hard to make heads or tails of all the technical blogs out there.

If you’re reading this article, you’re probably wondering whether or not you should learn JavaScript . Before we answer your question, we want to commend you for doing the research. It’s fun to learn new skills, and many people will jump right into a course. But, the most important step before you commit your time and energy to learning a new skill is making sure that it’ll support your goals.

Below, we’ll explain how learning JavaScript will help you reach your current goals. We’ll cover what type of work you can do with it, how long it takes to learn, where to get started, and more.

Why should I learn JavaScript?

JavaScript is one of the most popular coding languages , and together with HTML and CSS , it forms the base of modern web development. HTML codes the structure of a website, CSS dictates its style, and JavaScript enables its interactivity.

First and foremost, if you want to get into web development — both front-end and back-end engineering — JavaScript is a must. The language’s versatility means it can also be used for application design, animation, and game development . Plus, it’s easy to learn, so it’s a great choice as a first language. In another article, we take a closer look at what JavaScript is used for .

Another reason to learn JavaScript is that it opens you up to a giant community of developers that use the same language. If you have questions about a problem or need help debugging something, you’ll be able to collaborate with one of the largest groups of developers.

According to Stack Overflow’s 2020 Developer Survey , JavaScript was the most popular coding language for the eighth year in a row.

Is JavaScript the same as Java?

In short, no. JavaScript is the hugely popular web development language that is already installed on all common web browsers. It’s part of the reason why it’s so easy to get started with. You don’t need to configure or get familiar with an environment to code, unlike with Java . Java needs to be used within an environment that translates the code for the operating system (such as macOS, Windows, or Linux).

Java is a much more traditional coding language. It’s a class-based programming language and requires strict syntax to declare variables. Compared to JavaScript, it requires much more code to complete the same task. If you want to work in any of the following areas, Java will be a valuable addition to your repertoire:

Mobile development
Desktop application development
Back-end web development

As you can see, there’s some overlap between the applications of the two languages. For more information about how they’re distinct, learn about the differences between Java and JavaScript here .

How much does a JavaScript developer make?

As we explained earlier, JavaScript is commonly used for web development. Let’s take a look at the average salaries for web developers.

Front-End Developers

Front-End Developers create user interfaces and visual elements for web applications using JavaScript, CSS, and HTML. On average, Front-End Developers in the U.S. earn between $65k and $132k, depending on their experience.

Back-End Developers

Back-End Developers use JavaScript frameworks like Node.js and programming languages like SQL to manage an application’s servers and databases. Junior Back-End Developers in the U.S. average $78k, while more experienced Senior Back-End Developers earn around $120k.

Full-Stack Developers

Full-Stack Developers are proficient with both front-end and back-end development, and they can use any mix of the tools listed above. In the U.S., Full-Stack Developers can make anywhere between $79k and $130k.

How long does it take to learn JavaScript?

Most developers agree that it takes six to nine months to learn how to use JavaScript. Keep in mind that this is just an estimate, and everyone starts from a different level.

Learners who can commit themselves full-time to learning JavaScript may acquire proficiency faster than those with other responsibilities. Similarly, if you already have a solid coding background, you’ll pick up on the language quicker than someone new to programming.

Still, it’s not a race. Learning to code should be something you look forward to. You want to be able to approach your course with a positive outlook and a calm demeanor. Nothing makes it harder to debug a project and learn from your mistakes than being rushed or frustrated.

The six to nine-month timeframe relates to learning the basics of JavaScript. Other libraries use JavaScript as a base to create applications and webpages, including TypeScript , React , and Redux . Depending on the job you’re studying for or the new project you want to tackle, you may need to spend more time studying to be proficient with these libraries after you learn JavaScript.

Where can I learn JavaScript?

Once you’ve determined that JavaScript is the code you need to know, check out our Learn JavaScript course . We’ll teach you the language’s syntax and the basics of object-oriented programming.If you’re certain that you’d like to start training for a new career as a Front-End Developer, consider our Front-End Engineer Career Path . In addition to JavaScript, you’ll also learn programming languages like CSS and HTML and use them to build complete web applications.

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Posted on Apr 9, 2022 • Updated on Jul 22, 2022

33 JavaScript Concepts Every Developer Should Know 🤓️💯️

How much of JavaScript do you really think you know? You probably know how to write functions , understand simple algorithms , and can even write a class . But do you know what a typed array is?

You don't need to know all of these concepts right now, but you will eventually need them later in your career. That’s why I recommend bookmarking this list , because chances are, you’ll encounter one of these topics, and then you’re gonna want a tutorial to fully understand it.

It’s important to note that this list was inspired from the following repository:

Primitive Types
Value Types and Reference Types
Implicit, Explicit, Nominal, Structuring and Duck Typing
== vs === vs typeof
Function Scope, Block Scope and Lexical Scope
Expression vs Statement
IIFE, Modules and Namespaces
Message Queue and Event Loop
setTimeout, setInterval and requestAnimationFrame
JavaScript Engines
Bitwise Operators, Type Arrays and Array Buffers
DOM and Layout Trees
Factories and Classes
this, call, apply and bind
new, Constructor, instanceof and Instances
Prototype Inheritance and Prototype Chain
Object.create and Object.assign
map, reduce, filter
Pure Functions, Side Effects, State Mutation and Event Propagation
High Order Functions
Collections and Generators
async/await
Data Structures
Expensive Operation and Big O Notation
Inheritance, Polymorphism and Code Reuse
Design Patterns
Partial Applications, Currying, Compose and Pipe

1. Call Stack

A call stack is a mechanism for an interpreter (like the JavaScript interpreter in a web browser) to keep track of its place in a script that calls multiple functions — what function is currently being run and what functions are called from within that function, etc. — Source

📜 Understanding Javascript Call Stack, Event Loops — Gaurav Pandvia
📜 Understanding the JavaScript Call Stack — Charles Freeborn
📜 Javascript: What Is The Execution Context? What Is The Call Stack? — Valentino Gagliardi

2. Primitive Types

All types except objects define immutable values (that is, values which can't be changed). For example (and unlike in C), Strings are immutable. We refer to values of these types as "primitive values". — Source

📜 How numbers are encoded in JavaScript — Dr. Axel Rauschmayer
📜 What You Need to Know About JavaScript Number Type — Max Wizard K
📜 What Every JavaScript Developer Should Know About Floating Point Numbers — Chewxy

3. Value Types and Reference Types

Variables that are assigned a non-primitive value are given a reference to that value. That reference points to the object’s location in memory. The variables don’t actually contain the value. — Source

📜 Explaining Value vs. Reference in Javascript — Arnav Aggarwal
📜 Primitive Types & Reference Types in JavaScript — Bran van der Meer
📜 Value Types, Reference Types and Scope in JavaScript — Ben Aston

4. Implicit, Explicit, Nominal, Structuring and Duck Typing

Type coercion means that when the operands of an operator are different types, one of them will be converted to an "equivalent" value of the other operand's type. — Source

📜 What you need to know about Javascript's Implicit Coercion — Promise Tochi
📜 JavaScript Type Coercion Explained — Alexey Samoshkin
📜 Javascript Coercion Explained — Ben Garrison

5. == vs === vs typeof

JavaScript has two visually similar, yet very different, ways to test equality. You can test equality with == or ===. — Source

📜 JavaScript Double Equals vs. Triple Equals — Brandon Morelli
📜 Should I use === or == equality comparison operator in JavaScript? — Panu Pitkamaki
📜 == vs === JavaScript: Double Equals and Coercion — AJ Meyghani

6. Function Scope, Block Scope and Lexical Scope

It is important to make this distinction because expressions can act like statements, which is why we also have Expression statements. Though, on other the hand, statements cannot act like expressions. — Source

📜 JavaScript Functions—Understanding The Basics — Brandon Morelli
📜 The battle between Function Scope and Block Scope — Marius Herring
📜 Emulating Block Scope in JavaScript — Josh Clanton

7. Expression vs Statement

📜 All you need to know about Javascript's Expressions, Statements and Expression Statements — Promise Tochi
📜 Function Expressions vs Function Declarations — Paul Wilkins
📜 JavaScript Function — Declaration vs Expression — Ravi Roshan

8. IIFE, Modules and Namespaces

One of the often used coding patterns with functions has got a fancy name for itself: Immediately-invoked Function Expression. Or more dearly known as IIFE and pronounced as “iffy.” — Source

📜 Mastering Immediately-Invoked Function Expressions ― Chandra Gundamaraju
📜 Do ES6 Modules make the case of IIFEs obsolete?
📜 A 10 minute primer to JavaScript modules, module formats, module loaders and module bundlers ― Jurgen Van de Moere

9. Message Queue and Event Loop

“How is JavaScript asynchronous and single-threaded ?” The short answer is that JavaScript language is single-threaded and the asynchronous behaviour is not part of the JavaScript language itself, rather they are built on top of the core JavaScript language in the browser (or the programming environment) and accessed through the browser APIs. — Source

📜 JavaScript Event Loop Explained — Anoop Raveendran
📜 The JavaScript Event Loop: Explained — Erin Sweson-Healey
📜 Understanding JS: The Event Loop — Alexander Kondov

10. setTimeout, setInterval and requestAnimationFrame

We may decide to execute a function not right now, but at a certain time later. That’s called “scheduling a call”. — Source

📜 setTimeout and setInterval — JavaScript.Info
📜 Why not to use setInterval — Akanksha Sharma
📜 setTimeout VS setInterval — Develoger

11. JavaScript Engines

Writing code for the Web sometimes feels a little magical in that developers write a sequence of characters and like magic, those characters turn into concrete images, words, and actions within a browser. Understanding the technology can help developers better tune their craft as programmers. — Source

📜 JavaScript Engines — Jen Looper
📜 Understanding How the Chrome V8 Engine Translates JavaScript into Machine Code — DroidHead
📜 Understanding V8’s Bytecode — Franziska Hinkelmann

12. Bitwise Operators, Type Arrays and Array Buffers

Okay, so technically for the computer everything goes down to 1s and 0s. It does not operate with digits or characters or strings, it uses only binary digits (bits). The short version of this explanation is that everything is stored in binary form. Then the computer uses encodings such as UTF-8 to map the saved bit combinations to characters, digits or different symbols (the ELI5 version). — Source

📜 Programming with JS: Bitwise Operations — Alexander Kondov
📜 Using JavaScript’s Bitwise Operators in Real Life — ian m
📜 JavaScript Bitwise Operators — w3resource

13. DOM and Layout Trees

The Document Object Model, usually referred to as the DOM, is an essential part of making websites interactive. It is an interface that allows a programming language to manipulate the content, structure, and style of a website. JavaScript is the client-side scripting language that connects to the DOM in an internet browser. — Source

📜 How To Understand and Modify the DOM in JavaScript — Tania Rascia
📜 What’s the Document Object Model, and why you should know how to use it — Leonardo Maldonado
📜 JavaScript DOM Tutorial with Example — Guru99

14. Factories and Classes

JavaScript is a prototype-based language, meaning object properties and methods can be shared through generalized objects that have the ability to be cloned and extended. This is known as prototypical inheritance and differs from class inheritance. — Source

📜 How To Use Classes in JavaScript — Tania Rascia
📜 Javascript Classes — Under The Hood — Majid
📜 ES6 Classes — Nathaniel Foster

15. this, call, apply and bind

These functions are very important for every JavaScript Developer and are used in almost every JavaScript Library or Framework. — Source

📜 Grokking call(), apply() and bind() methods in JavaScript — Aniket Kudale
📜 How-to: call() , apply() and bind() in JavaScript — Niladri Sekhar Dutta
📜 JavaScript’s Apply, Call, and Bind Methods are Essential for JavaScript Professionals — Richard Bovell

16. new, Constructor, instanceof and Instances

Every JavaScript object has a prototype. All objects in JavaScript inherit their methods and properties from their prototypes. — Source

📜 JavaScript For Beginners: the ‘new’ operator — Brandon Morelli
📜 Let’s demystify JavaScript’s ‘new’ keyword — Cynthia Lee
📜 Constructor, operator "new" — JavaScript.Info

17. Prototype Inheritance and Prototype Chain

JavaScript is a bit confusing for developers experienced in class-based languages (like Java or C++), as it is dynamic and does not provide a class implementation per se (the class keyword is introduced in ES2015, but is syntactical sugar, JavaScript remains prototype-based). — Source

📜 Javascript : Prototype vs Class — Valentin PARSY
📜 JavaScript engine fundamentals: optimizing prototypes — Mathias Bynens
📜 JavaScript Prototype — NC Patro

18. Object.create and Object.assign

The Object.create method is one of the methods to create a new object in JavaScript. — Source

📜 Object.create in JavaScript — Rupesh Mishra
📜 Object.create(): the New Way to Create Objects in JavaScript — Rob Gravelle
📜 Basic Inheritance with Object.create — Joshua Clanton

19. map, reduce, filter

Even if you don’t know what functional programming is you’ve probably been using map, filter and reduce just because they’re so incredibly useful and make your code stink less by allowing you to write cleaner logic. — Source

📜 JavaScript Functional Programming — map, filter and reduce — Bojan Gvozderac
📜 Learn map, filter and reduce in Javascript — João Miguel Cunha
📜 JavaScript’s Map, Reduce, and Filter — Dan Martensen

20. Pure Functions, Side Effects, State Mutation and Event Propagation

So many of our bugs are rooted in IO related, data mutation, side effect bearing code. These creep up all over our code base—from things like accepting user inputs, receiving an unexpected response via an http call, or writing to the file system. Unfortunately, this is a harsh reality that we should grow accustomed to dealing with. Or is it? — Source

📜 Javascript and Functional Programming — Pure Functions — Omer Goldberg
📜 Master the JavaScript Interview: What is a Pure Function? — Eric Elliott
📜 JavaScript: What Are Pure Functions And Why Use Them? — James Jeffery

21. Closures

A closure is the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). In other words, a closure gives you access to an outer function's scope from an inner function. In JavaScript, closures are created every time a function is created, at function creation time. — Source

📜 I never understood JavaScript closures — Olivier De Meulder
📜 Understand JavaScript Closures With Ease — Richard Bovell
📜 Understanding JavaScript Closures — Codesmith

22. High Order Functions

JavaScript can accept higher-order functions. This ability to handle higher-order functions, among other characteristics, makes JavaScript one of the programming languages well-suited for functional programming. — Source

📜 Higher-Order Functions in JavaScript — M. David Green
📜 Higher Order Functions: Using Filter, Map and Reduce for More Maintainable Code — Guido Schmitz
📜 First-class and Higher Order Functions: Effective Functional JavaScript — Hugo Di Francesco

23. Recursion

Consider this post as a series of learning exercises. These examples are designed to make you think — and, if I’m doing it right, maybe expand your understanding of functional programming a little bit. — Source

📜 Recursion in JavaScript — Kevin Ennis
📜 Understanding Recursion in JavaScript — Zak Frisch
📜 Learn and Understand Recursion in JavaScript — Brandon Morelli

24. Collections and Generators

The Generator object is returned by a generator function and it conforms to both the iterable protocol and the iterator protocol. — Source

📜 ES6 In Depth: Collections — Jason Orendorff
📜 ES6 Collections: Using Map, Set, WeakMap, WeakSet — Kyle Pennell
📜 ES6 WeakMaps, Sets, and WeakSets in Depth — Nicolás Bevacqua

25. Promises

The Promise object represents the eventual completion (or failure) of an asynchronous operation and its resulting value. — Source

📜 JavaScript Promises for Dummies ― Jecelyn Yeen
📜 Understanding promises in JavaScript — Gokul N K
📜 Master the JavaScript Interview: What is a Promise? — Eric Elliott

26. async/await

There’s a special syntax to work with promises in a more comfortable fashion, called “async/await”. It’s surprisingly easy to understand and use. — Source

📜 Understanding async/await in Javascript — Gokul N K
📜 Exploring Async/Await Functions in JavaScript — Alligator.io
📜 Asynchronous Javascript using async/await — Joy Warugu

27. Data Structures

Javascript is evolving each day. With the rapid growth of frameworks and platforms like React, Angular, Vue, NodeJS, Electron, React Native, it has become quite common to use javascript for large-scale applications. — Source

📜 Data Structures in JavaScript — Thon Ly
📜 Algorithms and Data Structures in JavaScript — Oleksii Trekhleb
📜 Data Structures: Objects and Arrays ― Chris Nwamba

28. Expensive Operation and Big O Notation

“What is Big O Notation?” that is a very common job interview question for developers. In short, it is the mathematical expression of how long an algorithm takes to run depending on how long is the input, usually talking about the worst case scenario. — Source

📜 Big O Notation in Javascript — César Antón Dorantes
📜 Time Complexity/Big O Notation — Tim Roberts
📜 Big O in JavaScript — Gabriela Medina

29. Algorithms

Inheritance, Polymorphism and Code Reuse

In mathematics and computer science, an algorithm is a finite sequence of well-defined instructions, typically used to solve a class of specific problems or to perform a computation.

📜 Data Structures and Algorithms using ES6
📜 Algorithms and data structures implemented in JavaScript with explanations and links to further readings
📜 JS: Interview Algorithm

30. Inheritance, Polymorphism and Code Reuse

Class inheritance is a way for one class to extend another class, so we can create new functionality on top of the existing. — Source

📜 Inheritance in JavaScript — Rupesh Mishra
📜 Simple Inheritance with JavaScript — David Catuhe
📜 JavaScript — Inheritance, delegation patterns and Object linking — NC Patro

31. Design Patterns

Partial Applications, Currying, Compose and Pipe

Every developer strives to write maintainable, readable, and reusable code. Code structuring becomes more important as applications become larger. Design patterns prove crucial to solving this challenge - providing an organization structure for common issues in a particular circumstance. — Source

📜 4 JavaScript Design Patterns You Should Know — Devan Patel
📜 JavaScript Design Patterns – Beginner's Guide to Mobile Web Development — Soumyajit Pathak
📜 JavaScript Design Patterns — Akash Pal

32. Partial Applications, Currying, Compose and Pipe

Function composition is a mechanism of combining multiple simple functions to build a more complicated one. — Source

📜 Use function composition in JavaScript — Rémi
📜 Currying in JavaScript ES6 — Adam Bene
📜 Composition and Currying Elegance in JavaScript — Pragyan Das

33. Clean Code

Writing clean, understandable, and maintainable code is a skill that is crucial for every developer to master. — Source

📜 Clean Code Explained – A Practical Introduction to Clean Coding for Beginners — freeCodeCamp
📜 Clean Code concepts adapted for JavaScript — Ryan McDermott
📜 Clean Code Practice: How to write clean code — Tirth Bodawala

If you found this list useful, don’t forget to bookmark it and to follow me for more content like this.

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Top comments (16).

Templates let you quickly answer FAQs or store snippets for re-use.

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Can I translate it into Chinese? I will indicate the original link.

Joined Nov 12, 2021

Very nice selection!

Location Würzburg, Germany
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Joined Dec 4, 2019

A nice collection BUT.

Please carefully check your links and resources. I will dismiss any applicant that uses var or iffies without a very good reason. Articles that aim to extend knowledge should not use outdated syntax and especially not promote obsolete/legacy practices. The links regarding Design patterns are so outdated you could run them in IE6.

PLEASE don't promote legacy practices. Junior developers come here to seek best practices. These links teach ancient history.

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Hi, Good point! They probably reused an old post...

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Nice Selection!

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Very nicely explained!

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Oh wow. This is pretty impressive, thanks for your hard work!

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Thank you for your post!

Location Poland
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OMG! This is what I was looking for! Thank you for gathering this together!

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Learn Web Development Basics – HTML, CSS, and JavaScript Explained for Beginners

If you are learning web development, you will come across terms like HTML, CSS, and JavaScript. These are often called the building blocks of the Web.

These three tools dominate web development. Every library or tool seems to be centered around HTML, CSS, and JS. So if you want to become a web developer, you need to learn them well.

You'll also discover that websites are mostly built from these three languages.

But you're probably wondering what each one is and what it's really used for. What makes these languages so special and important? And what makes them so ubiquitous that you can’t help but see them in every tutorial and topic based on web development?

Well, now you need wonder no more.

In this article, I will explain the basics of what HTML, CSS, and JavaScript are, how they make the Web work, and what they do on their own.

What is the Internet?

The internet is simply a network of computers that communicate with each other to send and receive data (information).

Each of these computers on the internet can be distinguished and located by a unique number called an IP Address. An IP Address looks something like this: 168.212.226.204

What is the Web?

The Web is a subset of the internet.

Like every other computer network out there, the Web is made up of two main components: the web browser client and the web server.

The client requests the data and the server shares or serves its data. To achieve this, the two parties have to establish an agreement. That agreement is called the Application Programming Interface or in short, the API.

But this data has to be arranged and formatted into a form that's understandable by end-users who have a wide range of technical experiences and abilities.

This is where HTML, CSS, JavaScript and the whole concept of web development come into play.

What is HTML?

HTML stands for Hyper Text Markup Language.

Dictionary.com defines a Markup as:

a set of detailed instructions, usually written on a manuscript to be typeset, concerning style of type, makeup of pages, and the like.

So you can think of HTML as the language used for creating detailed instructions concerning style, type, format, structure and the makeup of a web page before it gets printed (shown to you).

But in the context of web development, we can replace the term ‘printed’ with ‘rendered’ as a more accurate term.

HTML helps you structure your page into elements such as paragraphs, sections, headings, navigation bars, and so on.

To illustrate what a page looks like, let's create a basic HTML document:

This is how you can format and structure a document with just HTML. As you can see, this markup contains some web elements such as:

Level 1 heading h1
Level 2 heading h2
Level 3 heading h3
A paragraph p
An unordered list with bullet points ul li
A button input input
And the whole body of the page body

This is what that markup above renders on a web browser:

You can also add attributes to these elements which you can use to identify the elements and access them from other places in the site.

In our example, we set the id attributes to all of the three span elements. This will help us access them from our JavaScript as you will see later.

Think of this attribute the same way as your social media username. With this name, others can find you on social media. And someone can also refer to you or mention you with this name (you can get tagged in a post, and so on).

This page is very basic and unattractive, though. If you are building anything other than a demo, you will need to add some basic styling to make it more presentable. And we can do exactly that with CSS.

Want to learn more about HTML? You can start with freeCodeCamp's Responsive Web Design certification and this brand new full HTML course from Beau Carnes .

What is CSS?

While HTML is a markup language used to format/structure a web page, CSS is a design language that you use to make your web page look nice and presentable.

CSS stands for Cascading Style Sheets , and you use it to improve the appearance of a web page. By adding thoughtful CSS styles, you make your page more attractive and pleasant for the end user to view and use.

Imagine if human beings were just made to have skeletons and bare bones – how would that look? Not nice if you ask me. So CSS is like our skin, hair, and general physical appearance.

You can also use CSS to layout elements by positioning them in specified areas of your page.

To access these elements, you have to “select” them. You can select a single or multiple web elements and specify how you want them to look or be positioned.

The rules that govern this process are called CSS selectors .

With CSS you can set the colour and background of your elements, as well as the typeface, margins, spacing, padding and so much more.

If you remember our example HTML page, we had elements which were pretty self-explanatory. For example, I stated that I would change the color of the level one heading h1 to red.

To illustrate how CSS works, I will be sharing the code which sets the background-color of the three levels of headers to red, blue, and green respectively:

The above style, when applied, will change the appearance of our web page to this:

Cool, right?

We access each of the elements we want to work on by "selecting" them. The h1 selects all level 1 headings in the page, the h2 selects the level 2 elements, and so on. You can select any single HTML element you want and specify how you want it to look or be positioned.

Want to learn more about CSS? You can check out the second part of freeCodeCamp's Responsive Web Design certification to get started.

What is JavaScript?

Now, if HTML is the markup language and CSS is the design language , then JavaScript is the programming language.

If you don’t know what programming is, think of certain actions you take in your daily life:

When you sense danger, you run. When you are hungry, you eat. When you are tired, you sleep. When you are cold, you look for warmth. When crossing a busy road, you calculate the distance of vehicles away from you.

Your brain has been programmed to react in a certain way or do certain things whenever something happens. In this same way, you can program your web page or individual elements to react a certain way and to do something when something else (an event) happens.

You can program actions, conditions, calculations, network requests, concurrent tasks and many other kinds of instructions.

You can access any elements through the Document Object Model API (DOM) and make them change however you want them to.

The DOM is a tree-like representation of the web page that gets loaded into the browser.

Thanks to the DOM, we can use methods like getElementById() to access elements from our web page.

JavaScript allows you to make your webpage “think and act” , which is what programming is all about.

If you remember from our example HTML page, I mentioned that I was going to sum up the two numbers displayed on the page and then display the result in the place of the placeholder text. The calculation runs once the button gets clicked.

This code illustrates how you can do calculations with JavaScript:

Remember what I told you about HTML attributes and their uses? This code displays just that.

The displaySum is a function which gets both items from the web page, converts them to numbers (with the Number method), sums them up, and passes them in as inner values to another element.

The reason we were able to access these elements in our JavaScript was because we had set unique attributes on them, to help us identify them.

So thanks to this:

We were able to do this:

Finally, upon clicking the button, you will see the sum of the two numbers on the newly updated page:

If you want to get started with JavaScript, you can check out freeCodeCamp's JavaScript Algorithms and Data Structures certification. And you can use this great Intro to JS course to supplement your learning.

How to Put HTML, CSS, and JavaScript Together

Together, we use these three languages to format, design, and program web pages.

And when you link together some web pages with hyperlinks, along with all their assets like images, videos, and so on that are on the server computer, it gets rendered into a website .

This rendering typically happens on the front end, where the users can see what's being displayed and interact with it.

On the other hand, data, especially sensitive information like passwords, are stored and supplied from the back end part of the website. This is the part of a website which exists only on the server computer, and isn't displayed on the front-end browser. There, the user cannot see or readily access that information.

Wrapping Up

As a web developer, the three main languages we use to build websites are HTML, CSS, and JavaScript.

JavaScript is the programming language, we use HTML to structure the site, and we use CSS to design and layout the web page.

These days, CSS has become more than just a design language, though. You can actually implement animations and smooth transitions with just CSS.

In fact, you can do some basic programming with CSS too. An example of this is when you use media queries, where you define different style rules for different kinds of screens (resolutions).

JavaScript has also grown beyond being used just in the browser as well. We now use it on the server thanks to Node.js .

But the basic fact remains: HTML, CSS, and JavaScript are the main languages of the Web.

So that's it. The languages of the Web explained in basic terms. I really hope you got something useful from this article.

To round off this article, I have something to share. I recently started a weekly coding challenge series aimed at teaching beginners how to program in JavaScript. Check it out on my blog .

Thank you for reading and see you soon.

P/S : If you are learning JavaScript, I created an eBook which teaches 50 topics in JavaScript with hand-drawn digital notes. Check it out here .

Helping you learn how to code one tutorial at a time. Online creator and entrepreneur.

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Analysis of JavaScript Programs: Challenges and Research Trends

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Bibliometrics & citations.

Bradley-Garcia M Bolton V (2023) Programming an n-Back task in Qualtrics using HTML and JavaScript The Quantitative Methods for Psychology 10.20982/tqmp.19.2.p136 19 :2 (136-155) Online publication date: 1-Feb-2023 https://doi.org/10.20982/tqmp.19.2.p136
Liu X Ziarek L (2023) PTDETECTOR: An Automated JavaScript Front-end Library Detector 2023 38th IEEE/ACM International Conference on Automated Software Engineering (ASE) 10.1109/ASE56229.2023.00049 (649-660) Online publication date: 11-Sep-2023 https://doi.org/10.1109/ASE56229.2023.00049
Zozas I Anagnostou I Bibi S (2023) Identify Javascript Trends in Crowdsourcing Small Tasks Evaluation of Novel Approaches to Software Engineering 10.1007/978-3-031-36597-3_9 (179-204) Online publication date: 8-Jul-2023 https://doi.org/10.1007/978-3-031-36597-3_9
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General and reference

Cross-computing tools and techniques

Verification

Software and its engineering

Software creation and management

Software development process management

Software verification and validation

Formal software verification

Software defect analysis

Software testing and debugging

Software notations and tools

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Software organization and properties

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Theory of computation

Semantics and reasoning

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Program analysis

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Program semantics

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Department of Computer and Information Science and Engineering / University of Florida / Gainesville, FL

Association for Computing Machinery

New York, NY, United States

Publication History

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analysis framework
dynamic analysis
security analysis
static analysis
web applications

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Korea Ministry of Education, Science and Technology (MEST)/National Research Foundation of Korea (NRF)
Samsung Electronics, and Google

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Nagy C Lanza M Cleve A (2023) Mining, Analyzing, and Evolving Data-Intensive Software Ecosystems Software Ecosystems 10.1007/978-3-031-36060-2_11 (281-314) Online publication date: 6-Oct-2023 https://doi.org/10.1007/978-3-031-36060-2_11
Cherry B Benats P Gobert M Meurice L Nagy C Cleve A (2022) Static Analysis of Database Accesses in MongoDB Applications 2022 IEEE International Conference on Software Analysis, Evolution and Reengineering (SANER) 10.1109/SANER53432.2022.00111 (930-934) Online publication date: Mar-2022 https://doi.org/10.1109/SANER53432.2022.00111
Karakochev A Zhang G (2021) Static Analysis of Large-Scale JavaScript Front End Web Engineering 10.1007/978-3-030-74296-6_36 (483-489) Online publication date: 18-May-2021 https://dl.acm.org/doi/10.1007/978-3-030-74296-6_36
Burnay N Lopes A Vasconcelos V (2020) Statically Checking REST API Consumers Software Engineering and Formal Methods 10.1007/978-3-030-58768-0_15 (265-283) Online publication date: 14-Sep-2020 https://dl.acm.org/doi/10.1007/978-3-030-58768-0_15
Liu X Woo G (2019) YapuresPlus Proceedings of the 2019 4th International Conference on Intelligent Information Technology 10.1145/3321454.3321472 (62-66) Online publication date: 20-Feb-2019 https://dl.acm.org/doi/10.1145/3321454.3321472
Welearegai G Schlueter M Hammer C Hung C Papadopoulos G (2019) Static security evaluation of an industrial web application Proceedings of the 34th ACM/SIGAPP Symposium on Applied Computing 10.1145/3297280.3297471 (1952-1961) Online publication date: 8-Apr-2019 https://dl.acm.org/doi/10.1145/3297280.3297471
Tiwari A Prakash J Gross S Hammer C (2019) LUDroid: A Large Scale Analysis of Android – Web Hybridization 2019 19th International Working Conference on Source Code Analysis and Manipulation (SCAM) 10.1109/SCAM.2019.00036 (256-267) Online publication date: Sep-2019 https://doi.org/10.1109/SCAM.2019.00036

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JavaScript Fundamentals

Let’s learn the fundamentals of script building.

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Interaction: alert, prompt, confirm
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Where Did I Put My Memory?

How paula poundstone learned to stop worrying about senior moments and enjoy being happily scatterbrained.

Paula Poundstone,

When my kids were little, if one of them said something like, “I told you I needed a carrot costume for school tomorrow,” I’d respond, “Did you see me write it down? If you didn’t see me write it down, it’s the same thing as not telling me. Go check the carrot costume drawer. See if there’s one in there.”

I’ve always forgotten stuff occasionally. In elementary school, I used to get in trouble for forgetting my sneakers for P.E. As punishment, the teacher made me sit on the retractable benches in the cafeteria/gym. I remember thinking, If I forget one more time, they’re gonna fold the bench back into the wall with me on it.

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But the day after the appearance of your first couple of gray hairs — I’m 64 now — any time you forget something, people start saying, “You’re having a senior moment.” Really? Then how do you explain all of the times I forgot stuff at 12, 17, 31 and 42 years old? There’s not a creature on earth more forgetful than a teenage boy. Have we forgotten that?

I’m no brain scientist, as far as I can remember, but I believe my inability to remember is stress-related. I’ll tell you what doesn’t improve your memory every time you forget something — worrying that it’s some kind of cognitive decline.

A while back, the University of Michigan's National Poll on Healthy Aging found that around half (48 percent) of people between age 50 and 64 were convinced they’d get dementia in their lifetime. But in reality, just 10 percent of Americans over 65 have some form of dementia. That means 40 percent of us are worrying about nothing. Nothing!

When my house was filled with kids and pets, and my nonlinear work as a stand-up comic and writer came with a wagonload of stress , I’d tape my to-do list to the front of my shirt. Anyone who saw it couldn’t help reading it.

“Did you buy a new drain stopper?” they’d ask.

“Oh, my gosh,” I’d respond. “I’ve gotta get to the hardware store!”

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I panic when I can’t remember stuff, and the panic causes whatever I’m trying to remember to continue eluding my consciousness. During the enormously stressful year that theaters were closed because of the COVID-19 pandemic, I volunteered every Saturday at a pop-up food bank in Santa Monica, California, where I live. One week they asked the volunteers to come on a Wednesday instead, which was no problem. While I was taking a break, leaning on a car in the parking lot and talking to a coworker, a friend came running up the street, waving a parking ticket he’d just found on his windshield.

I freaked out. I’d forgotten it was Wednesday because I was doing what I usually did on Saturdays. Why does that matter? Wednesdays are street-cleaning days in front of my house, where I usually park my car. If you don’t move your car, you get a $70 ticket. Like many of us, I had no income and no way of knowing when or if I ever would again. Plus, even on my best day, I don’t want a $70 parking ticket. So I was pretty upset.

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My friend suggested I move my car. “It’s too late,” I said, glancing at my watch. “I already got a ticket!” But then it occurred to me — how did I get here?

We were leaning on my car.

We struggle to keep things straight sometimes, so don’t overpack your burden bag with the idea that you’re in decline. Understand that, especially at this time in our history, we’re going through a lot. Breathe, exercise , talk with friends, drink water, listen to music, dance when no one is looking and, of course, laugh. (Did I tell you that already? I forgot.)

It’s also good to always put your keys in the same place.

Paula Poundstone is a stand-up comic, author and actor. She’s starred in two TV series, both called The Paula Poundstone Show. She currently hosts a weekly comedy podcast called Nobody Listens to Paula Poundstone and is a semiregular guest on the NPR podcast Wait Wait ... Don’t Tell Me!

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