Where Does JavaScript Run?

JavaScript is no longer limited to just web browsers. Thanks to modern tools and engines, JavaScript can run in many environments — from your browser to backend servers, even mobile apps and IoT devices.

🌐 1. In Web Browsers

This is the most common place where JavaScript runs. Every modern browser (Chrome, Firefox, Safari, Edge, etc.) comes with a built-in JavaScript engine:

• Chrome: V8
• Firefox: SpiderMonkey
• Safari: JavaScriptCore
• Edge: Chakra (older) / V8 (newer)

JavaScript in the browser powers things like: DOM manipulation, event handling, form validation, and client-side logic.

🖥️ 2. On Servers (Node.js)

Node.js is a runtime environment that allows JavaScript to run on the server-side, outside the browser. With Node.js, developers can build:

• Web servers and APIs
• Command-line tools
• Real-time apps (like chat)

It uses the same V8 engine as Chrome but adds modules for file systems, networking, databases, etc.

📱 3. In Mobile Apps

JavaScript can be used to build mobile apps using frameworks like:

• React Native: Native iOS/Android apps using React
• Ionic + Capacitor: Hybrid apps using web technologies
• Expo: Quick mobile development toolkit

🖥️ 4. On Desktop

Using Electron, JavaScript can power cross-platform desktop apps — like VS Code, Slack, or Discord.

📡 5. In IoT and Embedded Systems

Platforms like Johnny-Five and Espruino allow JavaScript to control hardware — sensors, motors, microcontrollers (like Arduino, Raspberry Pi, etc.).

🔁 Summary

JavaScript started in the browser but now runs nearly everywhere: