JavaScript
Introduction to JavaScript
JavaScript (JS) is the programming language of the web. While HTML provides structure and CSS provides style, JavaScript adds behavior — making pages interactive, dynamic, and powerful.
JavaScript runs directly in the browser without any setup required.
// Single-line comment
/* Multi-line comment */
// Output to the console (press F12 → Console tab to see it)
console.log("Hello, World!");
console.log(42);
console.log(true);
console.log([1, 2, 3]);
// Basic arithmetic operators
console.log(2 + 3); // 5 (addition)
console.log(10 - 4); // 6 (subtraction)
console.log(3 * 4); // 12 (multiplication)
console.log(15 / 4); // 3.75 (division)
console.log(15 % 4); // 3 (remainder/modulo)
console.log(2 ** 10); // 1024 (exponentiation)
// Comparison operators (return true or false)
console.log(5 > 3); // true
console.log(5 === "5");// false (strict equality: different types)
console.log(5 == "5"); // true (loose equality: coerces types — avoid!)
💡
Open the browser console now. Press F12 (or Cmd+Option+I on Mac), click the Console tab, and type any JavaScript expression. This is the fastest way to learn — experiment freely!
How to add JavaScript to a page:
<!-- At the end of <body> — ensures HTML is loaded first -->
<body>
<h1>My Page</h1>
<!-- Inline script (for small experiments) -->
<script>
console.log("Page loaded!");
</script>
<!-- External script file (recommended for real projects) -->
<script src="app.js" defer></script>
</body>
Watch & Learn
A recommended video to watch alongside this chapter.
More “Introduction to JavaScript” videos on YouTube