What is JavaScript?

What JavaScript is

JavaScript is the programming language of the web. Every major browser runs it, and Node.js runs it on servers. It powers interactivity on almost every website, so it works everywhere without installing anything.

JavaScript was created in 1995 by Brendan Eich while he worked at Netscape, the company behind an early popular web browser. It was written in a very short time so that web pages could respond to users. Despite the name, it is a different language from Java.

The language was standardized as ECMAScript by Ecma International in 1997, so every browser could follow the same rules. A large update in 2015, often called ES6 or ES2015, added classes, modules, arrow functions, and promises. The release of Node.js in 2009 let JavaScript run on servers as well as in browsers.

How JavaScript works

A web page is made of three parts. HTML gives it structure, CSS gives it style, and JavaScript gives it behavior. When a page loads, the browser reads the JavaScript and runs it with a built in program called a JavaScript engine.

JavaScript can read and change the page through the DOM, which is the browser's model of the page as a tree of elements. It listens for events such as clicks, key presses, and form submits, and runs functions in response. It can also request data from a server with the fetch function without reloading the page.

The language runs one thing at a time on a single main thread, and uses an event loop to handle waiting tasks. Slow work such as network requests is written as asynchronous code, using promises and the async and await keywords. Outside the browser, runtimes such as Node.js give JavaScript access to files, networks, and databases.

Key features of JavaScript

• Runs in every browser

  All major browsers include a JavaScript engine. Visitors do not need to install anything.

• Event driven

  Code reacts to user actions and other events. This suits interfaces, where most work happens in response to input.

• Asynchronous by design

  Promises and async functions let a program wait for slow tasks without freezing the page.

• Flexible typing

  Variables can hold any kind of value and types are checked while the program runs. This is quick to write but can hide mistakes.

• Huge package ecosystem

  The npm registry holds a very large number of reusable packages for nearly any task.

• Yearly language updates

  The standard is updated every year by a committee called TC39. New features are added without breaking old code.

When to use JavaScript

JavaScript compared with alternatives

How to start learning JavaScript

1. 01Learn basic HTML and CSS first so you have a page for your scripts to work on.
2. 02Follow the JavaScript guide on MDN Web Docs at developer.mozilla.org, or the free tutorial at javascript.info.
3. 03Practice in the browser console, which you can open with the developer tools in any browser.
4. 04Build small projects such as a counter, a to-do list, and a quiz to practice the DOM and events.
5. 05Learn fetch, promises, and async functions by showing data from a free public API on a page.

What JavaScript costs

JavaScript is free to use. It is an open standard, and the engines in browsers and runtimes such as Node.js are free as well. You only need a browser and a text editor to start.

How DATAL Projects uses JavaScript

JavaScript is part of our web development work in the Philippines. Common uses:

• Interactive website features
• Browser scripts and widgets
• Server code with Node.js

Common questions about JavaScript