Online JavaScript Compiler & Algorithm Visualizer – Run JS Online (Node 18, 20, 21)
Write, compile, and run JavaScript code instantly in your browser. This free online JavaScript compiler needs no installation or signup — just type your JavaScript program, click Run, and see the output. Supports stdin, multi‑file projects, shareable snippet URLs, and AI help to generate, fix, and explain JavaScript code.
About Online Compiler
Our free online compiler lets you write, compile, and run code instantly in your browser. Supports Python, Java, C++, JavaScript, Go, Rust, and many more languages. No installation required.
Compare Languages Side by Side
Want to see how Javascript stacks up against another language? Open the Code Playground to run Javascript next to Python, Go, Rust, or any language — each pane picks its own language and version, and you run them together.
Supported Languages
Popular: Python, Java, C++, C, JavaScript, TypeScript, Go, Rust
Web: PHP, Ruby, Node.js, HTML/CSS
Systems: C, C++, Rust, Go, Swift
Functional: Haskell, Scala, Kotlin, F#, Clojure
Features
- Monaco Editor (VS Code) with syntax highlighting
- Real-time code execution with output streaming
- Custom compiler flags support (-O2, -Wall, etc.)
- Share code via unique snippet URLs
- Keyboard shortcuts (Ctrl+Enter to run)
Run & Visualize JavaScript (Node.js) Online (18, 20, 21)
Execute Node.js scripts in your browser using versions 18, 20, or 21. Plus a built‑in algorithm visualizer: click Visualize to watch your code run line by line as arrays, 2D matrices, Map, Set, linked lists, and binary trees animate step by step — with a call‑stack view for recursion. Ideal for learning sorting, binary search, recursion, BST/tree traversals, and frequency counting. Multi‑file, stdin, and shareable snippet URLs supported.
FAQ
Does the online JavaScript compiler include an algorithm visualizer? Yes. Click Visualize to step through your code while arrays, matrices, Maps, Sets, linked lists, and trees animate — a built‑in JavaScript visualizer that highlights each read and write, the current line, and the call stack for recursion.
Which data structures and algorithms can I visualize? Arrays and 2D arrays, Map and Set, and object‑based linked lists and binary trees ({ val, next } / { val, left, right }) — great for sorting, binary search, counting (count[x]++), recursion, and BST/tree traversals.
Which Node.js versions are available? Node.js 18, 20, and 21 are available.
How do I share code? Click Share to generate a permalink for your snippet.
Should I use TypeScript? For TS, use the TypeScript page which compiles TS 5.3 on Node 20.
How to Use Online Compiler
Choose from 60+ programming languages including Python, Java, C++, JavaScript, Go, Rust, and more.
Use our Monaco editor (same as VS Code) with syntax highlighting, auto-completion, and error detection.
Click Run or press Ctrl+Enter. Your code executes in a secure sandbox and output appears instantly.
Share your code via unique URL or embed interactive code snippets in your blog, book, or documentation.
For Authors, Educators & Technical Writers
Perfect for programming books, online tutorials, technical documentation, and educational content. Embed interactive, runnable code examples directly in your content.
Click Embed button above to generate embed code for your content!
Example: Hello World in JavaScript
function greet(name) {
return `Hello, ${name}!`;
}
console.log(greet("World"));Copy this JavaScript snippet into the editor above and click Run to execute it instantly — no setup required.
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Need embeds? See Embed Online Compiler.