Basics

What is JavaScript?

The programming language of the web — runs in browsers and on servers.

1. Explanation

JavaScript is a high-level, interpreted programming language created by Brendan Eich in 1995. It runs natively in every web browser and on servers via Node.js. JavaScript adds interactivity to web pages — handling clicks, validating forms, fetching data, animating elements and building full applications. Together with HTML (structure) and CSS (style), JavaScript (behavior) makes up the foundation of the modern web.

2. Syntax

<script>
  // your JavaScript here
</script>

3. Example

Try it yourself

// You can put JS inside an HTML file or in a .js file
console.log("Hello, JavaScript!");

// Change a heading on the page
document.title = "JS is awesome";

Console

Click Run to see output.

4. Expected output

output

Hello, JavaScript!

5. Common mistakes

✗Forgetting to link the .js file with <script src="app.js"></script>
✗Placing the <script> tag in <head> without 'defer', causing it to run before the DOM exists
✗Confusing JavaScript with Java — they are completely different languages

6. Practice questions

Create an HTML file that loads a script and logs your name to the console
Use console.log to print the result of 5 + 7
Change document.title to your favorite quote

→ Try more practice problems

7. Mini project

Hello User

Prompt the user for their name and greet them.

const name = prompt("What's your name?");
alert("Hello, " + name + "!");