academy rtl theme React is a JavaScript library used in web development to build interactive elements on websites. But if you’re not familiar with JavaScript or JavaScript libraries, that’s not a helpful definition. So let’s take a step back and deal with those terms first.
What is JavaScript?
You can read all about JavaScript in our complete Tech 101 JavaScript guide, but here’s the TLDR:
- JavaScript (or JS) is a scripting language used to create and control dynamic web content.
- Dynamic web content includes things like animated graphics, photo slideshows, and interactive forms.
- Anytime you visit a website where things move, refresh, or otherwise change on your screen without requiring you to manually reload a web page, there’s a very good chance JS is the language making it happen.
Or try this one sentence definition: JavaScript is a super important coding language used to add animated and interactive features to websites or web applications (on top of the basic, static structures created by languages like HTML and CSS).
What is a JavaScript library?
From the definition above, you can see how JavaScript plays a critical role in website and web application development. But there are times when you need JavaScript to perform repetitive functions — things like stock animation effects or autocomplete search bar features. Re-coding these functions every time they occur becomes a “reinventing the wheel” situation. Annnnoying. This is where JavaScript libraries come in.
JavaScript libraries are collections of pre-written JavaScript code that can be used for common JS tasks, allowing you to bypass the time intensive (and unnecessary) process of coding by hand. If there’s a run-of-the-mill JavaScript function that you keep needing to code (and that other developers before you have needed for their own projects) there’s probably a JS library to ease your pain. Make sense?
OK, so let’s get back to React. There are a lot of different JS libraries out there and React JS is one of them — but what makes it unique? What is React JS used for, and why should you learn React JS? And is it better than other JavaScript libraries?
Why Do JavaScript Developers Use React JS?
React is a JavaScript library that specializes in helping developers build user interfaces, or UIs. In terms of websites and web applications, UIs are the collection of on-screen menus, search bars, buttons, and anything else someone interacts with to USE a website or app.
Note: readers often ask “is React JS frontend or backend?” The answer is: definitely frontend. You can keep this straight by remembering the “on screen” aspect of UIs — React is used exclusively for “client side” programming (building things that a user will see on screen in their browser window), which makes React JS a frontend library.
Before React JS, developers were stuck building UIs by hand with “vanilla JavaScript” (developer speak for the raw JavaScript language on its own) or with less UI-focused React predecessors like jQuery. That meant longer development times and plenty of opportunities for errors and bugs. So, in 2011, Facebook engineer Jordan Walke created React JS(opens in a new tab) specifically to improve UI development.
In addition to providing reusable React library code (saving development time and cutting down on the chance for coding errors), React comes with two key features that add to its appeal for JavaScript developers:
- JSX
- Virtual DOM
To get an even better understanding of React JS and why you should use it, let’s take a look at both.
JSX
At the heart of any basic website are HTML documents. Web browsers read these documents and display them on your computer, tablet, or phone as web pages. During this process, browsers create something called a Document Object Model (DOM), a representational tree of how the web page is arranged. Developers can then add dynamic content to their projects by modifying the DOM with languages like JavaScript.
JSX (short for JavaScript eXtension) is a React extension that makes it easy for web developers to modify their DOM by using simple, HTML-style code. And — since React JS browser support extends to all modern web browsers — JSX is compatible with any browser platform you might be working with.
This isn’t just a matter of convenience, though — using JSX to update a DOM leads to significant site performance improvements and development efficiency. How? It’s all about the next React feature, the Virtual DOM.
Virtual DOM
If you’re not using React JS (and JSX), your website will use HTML to update its DOM (the process that makes things “change” on screen without a user having to manually refresh a page). This works fine for simple, static websites, but for dynamic websites that involve heavy user interaction it can become a problem (since the entire DOM needs to reload every time the user clicks a feature calling for a page refresh).
However, if a developer uses JSX to manipulate and update its DOM, React JS creates something called a Virtual DOM. The Virtual DOM (like the name implies) is a copy of the site’s DOM, and React JS uses this copy to see what parts of the actual DOM need to change when an event happens (like a user clicking a button).
Let’s say a user enters a comment in a blog post form and pushes the “Comment” button. Without using React JS, the entire DOM would have to update to reflect this change (using the time and processing power it takes to make this update). React, on the other hand, scans the Virtual DOM to see what changed after a user action (in this case, a comment being added) and selectively updates that section of the DOM only.
This kind of selective updating takes less computing power and less loading time, which might not sound like much when you’re talking about a single blog comment, but — when you start to think about all the dynamics and updating associated with even a slightly complex website — you’ll realize it adds up to a lot.
