Introduction to JavaScript

What is JavaScript?

JavaScript is a programming language primarily used to make web pages dynamic and interactive.
Unlike HTML (content structure) and CSS (styling and layout), JavaScript handles the logic and behavior of a page.

It can run:

In the browser (Chrome, Firefox, Safari, Edge) to manipulate a web page.
Outside the browser with Node.js to build servers, scripts, or desktop applications.

A brief history

1995: Created by Brendan Eich at Netscape in just 10 days.
Initially called Mocha, then LiveScript, and finally JavaScript (to capitalize on Java’s popularity at the time).
Today, it is standardized by ECMA International under the official name ECMAScript (ES).
The most widely used version today is ES6+ (ECMAScript 2015 and later).

Main roles

Manipulating the DOM (HTML page content).
Responding to events (clicks, keyboard input, etc.).
Communicating with a server via APIs (AJAX, fetch, WebSockets).
Creating animations and visual effects.
Building server-side applications (e.g., with Node.js).
Developing mobile and desktop apps (e.g., with React Native, Electron).

Simple example

<!DOCTYPE html>
<html>
  <body>
    <h1 id="title">Bonjour</h1>
    <button onclick="changeText()">Click me</button>

    <script>
      function changeText() {
        document.getElementById("title").innerText = "Hello, JavaScript!";
      }
    </script>
  </body>
</html>

Summary

JavaScript complements HTML + CSS to create rich web experiences.
It is a universal language today, used for both front-end and back-end development.
It is used for everything: websites, mobile apps, servers, games, and more.