Online JavaScript Playground: Write, Run, Share Instantly
The fastest way to write and run JavaScript in your browser. No setup, instant execution, live preview.
# Online JavaScript Playground: Write, Run, Share Instantly
You have a JavaScript idea. Maybe it is a quick algorithm to test, a library to try out, or a concept to explain to a colleague. You do not want to open a terminal, scaffold a project, or configure a bundler. You want to type code and see it run.
[YaliCode](https://yalicode.dev) gives you two ways to run JavaScript in your browser: server-side Node.js execution for scripts and algorithms, and WebContainer-based environments for full frontend projects with live preview.
Getting Started in 10 Seconds
1. Open [yalicode.dev/editor](https://yalicode.dev/editor)
2. Select the JavaScript template
3. Write your code
4. Press Ctrl+Enter to run
That is it. No account required, no installation, no configuration.
```javascript
// Your first JavaScript snippet on YaliCode
const languages = ['Python', 'JavaScript', 'Rust', 'Go', 'TypeScript'];
const sorted = languages.sort((a, b) => a.length - b.length);
console.log('Sorted by name length:', sorted);
```
Output appears instantly in the console panel below the editor. Standard output is displayed in white, errors in red, and system messages in gray.
Two Runtimes, One Editor
YaliCode supports JavaScript through two distinct runtimes, each optimized for different use cases.
Node.js Server-Side Execution
When you select the JavaScript template and press Ctrl+Enter, your code runs in a sandboxed Docker container with Node.js on our servers. This is ideal for:
```javascript
// Async/await example
async function fetchData() {
const delay = (ms) => new Promise(resolve => setTimeout(resolve, ms));
console.log('Starting...');
await delay(500);
console.log('Processing...');
await delay(500);
console.log('Done!');
return { status: 'complete', timestamp: Date.now() };
}
fetchData().then(result => console.log(result));
```
Server-side execution gives you accurate timing, proper process behavior, and access to Node.js standard library modules. Results are cached, so running the same deterministic code twice returns the result instantly.
WebContainer Frontend Runtime
For frontend projects that need a browser environment, select any of our frontend templates: React, Vue, Svelte, Next.js, Angular, or Astro. These run entirely in your browser tab using WebContainers.
The WebContainer runtime provides:
```jsx
// React component — runs in WebContainer with live preview
import { useState } from 'react';
export default function Counter() {
const [count, setCount] = useState(0);
return (
<div style={{ padding: '2rem', fontFamily: 'sans-serif' }}>
<h1>Count: {count}</h1>
<button onClick={() => setCount(c => c + 1)}>Increment</button>
<button onClick={() => setCount(0)}>Reset</button>
</div>
);
}
```
Changes reflect in the preview panel as you type. There is no save-and-refresh cycle.
Using npm Packages
In WebContainer Templates
Frontend templates have a `package.json`. Add any npm package and the WebContainer will install it:
```json
{
"dependencies": {
"lodash": "^4.17.21",
"axios": "^1.7.0",
"date-fns": "^3.6.0"
}
}
```
You can also use the built-in Package Manager panel in the sidebar to search npm packages and add them to your project without editing JSON files manually.
In Server-Side Execution
For Node.js execution, YaliCode supports dependency installation when explicitly enabled. Add a `requirements` comment or use the dependency panel to specify packages. The sandbox briefly enables network access to install packages, then locks it down before running your code.
Console Output and Stdin
The console panel captures everything your code writes to `stdout` and `stderr`. For interactive programs that read from `stdin`, YaliCode shows a dialog where you can enter input before execution.
```javascript
// Reading user input
const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
rl.question('Enter a number: ', (answer) => {
const n = parseInt(answer);
console.log(`${n} squared is ${n * n}`);
rl.close();
});
```
When you run this, a stdin dialog appears. Type your input, submit it, and the program executes with that input provided.
AI-Powered Features
The [YaliCode editor](https://yalicode.dev/editor) includes AI features that make JavaScript development faster:
Inline Code Completion
As you type, ghost text suggestions appear ahead of your cursor. Press Tab to accept a suggestion. The AI understands your current file context and suggests relevant completions.
Error Explanation
When your code throws an error, click the "Explain Error" button in the console panel. You get a plain-language explanation of what went wrong and a suggested fix.
Code Chat
Open the AI panel from the sidebar to ask questions about your code. The AI can explain algorithms, suggest optimizations, and help you debug tricky issues.
Sharing and Collaboration
Every saved project on YaliCode gets a public URL:
```
https://yalicode.dev/p/yourname/fizzbuzz-solution
```
Anyone with the link can view your code, fork it into their own account, and run it. This makes YaliCode useful for:
For real-time collaboration, YaliCode supports multiplayer editing. Invite collaborators to your project and edit the same file simultaneously. Changes are synchronized in real time using conflict-free replicated data types (CRDTs), so there are no merge conflicts.
Keyboard Shortcuts
Efficient coding means keeping your hands on the keyboard. Here are the essential shortcuts:
| Shortcut | Action |
|----------|--------|
| Ctrl+Enter | Run code |
| Ctrl+S | Save project |
| Ctrl+/ | Toggle line comment |
| Shift+Alt+F | Format code (Prettier) |
| Ctrl+Shift+P | Command palette |
| Ctrl+D | Select next occurrence |
| Ctrl+` | Toggle terminal panel |
Debugging JavaScript
Set breakpoints by clicking the gutter next to a line number. When you run the code, the debugger captures variable values at each breakpoint. The debug panel shows:
```javascript
function fibonacci(n) {
// Set a breakpoint here to watch values
if (n <= 1) return n;
return fibonacci(n - 1) + fibonacci(n - 2);
}
console.log(fibonacci(10)); // 55
```
The debugger uses trace-based instrumentation rather than a traditional step debugger. Your code runs once, and all breakpoint hits are captured for inspection after execution completes.
Start Building
Whether you need a quick scratchpad for algorithm practice or a full React project with live preview, [YaliCode](https://yalicode.dev/editor) has you covered. Open the editor, pick JavaScript, and start writing. Your code runs in under two seconds.
No downloads. No configuration. No waiting.