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What is JavaScript and why should I learn it?

Everything you need to know about JavaScript and its role as the world's most popular web programming language

JavaScript is one of the three non-negotiable languages in which front-end developers absolutely must be proficient to be relevant in today’s job market. HTML and CSS used to be the only two languages required to build a website, but JavaScript has propelled web development into a new era.

With JavaScript, developers are equipped with the power to create dynamic, responsive web pages and the ability to bring complex and genuinely intriguing ideas to life within a web browser. With modern websites all leveraging the power of JavaScript, a website that doesn’t feature JavaScript code is immediately noticeable with an obviously dated feel.

What is JavaScript?

JavaScript is essentially a programming language that simplifies the building and designing of websites, while also ensuring they're tooled up to be as engaging and attractive as possible. It shouldn't be confused with Java, however, which is a completely separate programming language.

It’s also widely regarded as one of the most beginner-friendly languages to learn, one that doesn’t involve a steep learning curve, making it an ideal entry point into the world of programming and web development. It’s also immensely popular. Developer haven Stack Overflow recently announced it was the most-used programming language in the world for the tenth year running, with more than 65% of developers surveyed saying they use the technology either professionally or as part of personal projects.

JavaScript is more than a language, too, it’s also a huge family of programming frameworks and the muse for other languages like TypeScript. Frameworks provide collections of pre-written, oft-used JavaScript code to more easily build applications using JavaScript, and there are many to choose from - although some of the most popular are React, Vue, Angular, and Node.js.

Should I learn JavaScript?

JavaScript is absolutely essential in the present job market for web developers, and most employers will not employ even the most junior of web developers without some skills in the language. Proficiency in HTML, CSS, and JavaScript are all necessary to land a web developer position in today’s climate.

Before learning any programming language, it's important to understand what you want to achieve in programming. So, if you want to build websites, the aforementioned trio of languages form the essential base-level skills before other technologies are mastered such as SQL, NoSQL, and other JavaScript frameworks. 

If you want to pursue the software development route, JavaScript may not necessarily be the optimal first choice of language, though many do recommend it as a first language regardless. This is because it can ease newcomers into the fundamentals of programming - structuring code, familiarity with data structures, and more - while not being overly complex.

JavaScript skills can also be transferred to software development when using frameworks such as React Native, which has traditionally been used to build cross-platform mobile apps from the same code base, for example. That said, if you’re trying to get a software development job as quickly as possible, there may be better first-time languages to learn.

How does JavaScript work?

Going back to the core trio of web development languages - HTML, CSS, and JavaScript - you can think of HTML as the one that’s responsible for putting the basic data on the web page, such as text. CSS is the styling component: it tells the browser how far apart to space text and images, for example. JavaScript is responsible for handling dynamic components like animations, live multimedia, triggering functions on button clicks, and other interactive elements every web user expects from a contemporary website.

Unlike many software development languages, JavaScript is not a compiled language. That is to say JavaScript code isn’t sent to a ‘compiler’ which then turns the human-readable code produced by a programmer into machine code, or bytecode - a way for the computer itself to understand what the human programmer wants a web page to do.

Instead, JavaScript is an interpreted language, which means the web browser parses each line of JavaScript code in the order in which it was written and runs it, as is.

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When a web page is opened, the HTML code is parsed into the browser’s document object model (DOM) - the component that tells a browser what data to place on the page. The CSS code is then processed using the browser’s CSS parser, informing the layout for the data supplied by the HTML code. Once the essential information is on the page, this is then shown to the JavaScript code, the job of which is to change what’s already on a web page, make it look better and provide more interactive elements. It can’t do this without any content present, which is why JavaScript is run after the HTML and CSS.

Rather than the traditional line-by-line parsing of JavaScript, it’s common for browsers to compile its code before running it. Many modern browsers employ a technology called just-in-time (JIT) compilation which compiles JavaScript into machine code before it runs as a way of improving speed and performance. That said, it’s not true code compilation in the same way that software is compiled as an entire code base before running. The JIT compiler takes JavaScript as it’s just about to run and is able to optimise it differently for each web user, making sure that no matter what device a web page is being accessed from, users can get the same great browsing experience.

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