1. Definition

JavaScript in the browser runs inside a web browser and is used to create interactive user interfaces. Node.js allows JavaScript to run outside the browser, mainly on the server side to build backend applications.

2. Where it Runs

• Browser JS: Runs inside web browsers like Chrome, Edge
• Node.js: Runs on the server (outside browser)

3. API Access

• Browser JS: Can access DOM, window, document
• Node.js: Cannot access DOM, but has file system, OS, network APIs

4. Use Cases

• Browser JS: UI interactions, animations, form validation
• Node.js: Backend logic, APIs, database handling

5. Example

Browser JavaScript:

document.getElementById("btn").addEventListener("click", () => {
  alert("Button clicked!");
});

Node.js:

const fs = require("fs");

fs.writeFileSync("test.txt", "Hello from Node.js");

6. Key Differences

• Browser JS works with UI, Node.js works with server
• Browser has DOM access, Node.js does not
• Node.js can access system resources
• Both use JavaScript but in different environments