Hello World in JavaScript

Every programming journey starts with Hello World. JavaScript makes this remarkably simple - just one line using the console.log() function.

The Code

Create a file named hello.js:

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console.log("Hello, World!");

That’s it! One line, no boilerplate, no imports required.

Understanding the Code

• console.log() - A built-in function that outputs text to the console
• "Hello, World!" - A string literal enclosed in double quotes
• No semicolon required - JavaScript has automatic semicolon insertion (ASI), though many developers add them explicitly
• No main function - JavaScript executes code from top to bottom

Running with Docker

The easiest way to run JavaScript without installing Node.js locally:

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# Pull the official Node.js Alpine image
docker pull node:22-alpine

# Run the program
docker run --rm -v $(pwd):/app -w /app node:22-alpine node hello.js

Running Locally

If you have Node.js installed (v18+):

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# Run directly with Node.js
node hello.js

Expected Output

Hello, World!

Running in the Browser

JavaScript is unique - it can run directly in your web browser. Open your browser’s Developer Tools (F12 or Cmd+Option+I on Mac) and type in the Console:

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console.log("Hello, World!");

You’ll see the output immediately. This is the JavaScript REPL (Read-Eval-Print Loop).

Alternative Ways to Print

JavaScript offers several ways to output text:

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// Standard console output
console.log("Hello, World!");

// With formatting (in browsers)
console.info("Information message");
console.warn("Warning message");
console.error("Error message");

// In a browser, you can also use:
// alert("Hello, World!");  // Shows a popup dialog
// document.write("Hello, World!");  // Writes to the page

Why JavaScript Stands Out

Compare JavaScript’s Hello World to other languages:

JavaScript and Python tie for simplicity, but JavaScript has the unique advantage of running in every web browser without any installation.

Key Concepts

1. JavaScript is interpreted - No compilation step; code runs directly
2. Dynamic typing - Variables don’t need type declarations
3. Runs everywhere - Browsers, servers (Node.js), mobile (React Native), desktop (Electron)
4. Event-driven - JavaScript excels at handling user interactions and async operations

Modern JavaScript Features

Even in a simple Hello World, you could use modern syntax:

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// Using template literals (ES6+)
const greeting = "World";
console.log(`Hello, ${greeting}!`);

// Using arrow functions
const sayHello = () => console.log("Hello, World!");
sayHello();

The Node.js REPL

You can also use Node.js interactively:

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docker run --rm -it node:22-alpine node

Then type:

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> console.log("Hello, World!")
Hello, World!
undefined
> .exit

The undefined you see is the return value of console.log() - it prints the message but returns nothing.

Next Steps

Continue to Variables and Data Types to learn about storing and manipulating data in JavaScript.