An Introduction to JavaScript

JavaScript (often abbreviated as JS) is a high-level, interpreted programming language that makes web pages interactive. Alongside HTML and CSS, it is one of the three core technologies of the World Wide Web.

What is JavaScript?

JavaScript was created by Brendan Eich in 1995 while working at Netscape. Originally called Mocha, then LiveScript, it was renamed to JavaScript as a marketing move during the rise of Java.

Today, JavaScript runs everywhere - browsers, servers (Node.js), mobile apps, desktop applications, and even IoT devices.

Here’s a simple taste of JavaScript:

<p id='demo'></p>

document.getElementById('demo').textContent = 'Hello, JavaScript!';

What can JavaScript do?

• DOM Manipulation - change HTML and CSS on the fly
• Event Handling - respond to clicks, keystrokes, form submissions
• API Calls - fetch data from servers
• Animations - create smooth visual effects
• Full-stack development - build servers with Node.js, Deno, Bun

What CAN’T JavaScript do?

• File system access (in the browser) - browsers sandbox JS for security
• Raw network access - no low-level socket control without APIs
• Multithreading - JavaScript is single-threaded (but has Web Workers)

Manuals and Specifications

When learning JavaScript, these resources are essential:

The language is formally called ECMAScript (ES). The version matters:

Code Editors

You need a good editor to write JavaScript. Here are popular choices:

For this tutorial series, VS Code is recommended. Key extensions:

• ESLint - catches errors as you type
• Prettier - auto-formats your code
• JavaScript (ES6) code snippets - boosts productivity

Developer Console

Every browser has a Developer Console where you can experiment with JavaScript in real-time.

How to open it

Using the Console

The console is a REPL (Read-Eval-Print-Loop). You type JavaScript, it runs immediately:

console.log("Hello from the console!");
// → Hello from the console!

2 + 2
// → 4

typeof "hello"
// → "string"

Try pasting this in your console:

console.log('This appears in the console tab!');
console.warn('This is a warning');
console.error('This is an error');
console.table([{name: 'Alice', age: 30}, {name: 'Bob', age: 25}]);

Pro tip: Use console.log() frequently while learning - it’s your best debugging friend.

Console Methods

console.time("loop");
for (let i = 0; i < 1000000; i++) {}
console.timeEnd("loop");
// → loop: 2.45ms