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How do I run JavaScript or TypeScript in my browser?

Type or paste JavaScript or TypeScript code in the editor and click Run to execute it instantly with console output. The tool captures console.log, errors, and return values in a built-in console. Choose from example snippets to get started. Everything runs in a sandboxed environment in your browser.

Run JavaScript instantly
Input
const nums = [1, 2, 3, 4, 5];
const sum = nums.reduce((a, b) => a + b, 0);
console.log("Sum:", sum);
console.log("Avg:", sum / nums.length);
Output
Sum: 5
Avg: 3
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JavaScript / TypeScript Playground

Write and run JavaScript or TypeScript code directly in your browser. No setup required.

Ctrl+Enter to run · Tab inserts spaces

Console Output

Click Run or press Ctrl+Enter to execute your code

Tips & Best Practices

Pro Tip

Use console.table() for arrays and objects in the playground

console.log() outputs messy nested objects. console.table() renders arrays of objects as formatted tables, making it far easier to compare values. Also try console.dir() for interactive tree views of DOM elements and complex objects.

Common Pitfall

Top-level await requires module mode or async wrapper

If your code uses `await fetch(...)` at the top level, it needs to run in a module context or be wrapped in an async IIFE: `(async () => { const data = await fetch(...); })()`. Most playgrounds don't enable module mode by default.

Real-World Example

Test array methods by chaining .map(), .filter(), .reduce()

The playground is perfect for experimenting with functional array patterns. Try: `[1,2,3,4,5].filter(n => n % 2).map(n => n ** 2).reduce((a,b) => a+b, 0)` — understanding this chain is fundamental to modern JavaScript.

Security Note

Browser playgrounds sandbox code — but be careful with production data

Client-side JS playgrounds run code in your browser, not a server. But code you paste may contain API keys, tokens, or credentials. DevBolt never sends your code anywhere, but always scrub sensitive data from code snippets before testing.

Frequently Asked Questions

Can I run TypeScript in a browser-based JavaScript playground?
Yes, DevBolt's JavaScript Playground supports TypeScript by transpiling it to JavaScript before execution. Type annotations, interfaces, enums, generics, and other TypeScript features are processed and stripped during transpilation. Type errors are reported in the output panel. This is useful for testing TypeScript snippets, experimenting with type patterns, and prototyping without setting up a local project. The playground captures console.log output and handles async/await.
Is code executed in a browser playground safe and sandboxed?
Browser-based playgrounds run code in a sandboxed environment preventing access to the file system, other tabs, and system resources. DevBolt's playground runs code in an isolated context where console methods are intercepted to display output. Avoid running untrusted code as it could still make network requests or consume CPU. The playground includes execution timeout protection to prevent runaway scripts from freezing your browser tab.
What is the difference between running JavaScript in a playground vs Node.js?
A browser playground provides Web APIs (DOM, fetch, localStorage, Canvas) while Node.js provides server-side APIs (fs, http, path, child_process). Module systems differ: browsers use ES modules natively while Node.js supports both CommonJS and ES modules. Browser playgrounds cannot access the file system or spawn processes. Both environments share the same ECMAScript core. For testing pure logic and algorithms, a browser playground works perfectly. For file I/O and server code, you need Node.js.

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