Hello, World
console.log("Hello, World!");1 file
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main.ts · output appears here
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Output streams here as your program runs.
Bun 1.3.14Readymain.tsLn 1, Col 1Spaces: 4UTF-8
Tap Run to execute
main.ts · output appears here
Press Run to execute
Output streams here as your program runs.
Bun is a fast, all-in-one JavaScript and TypeScript runtime built on Apple's JavaScriptCore engine. It runs JS and TS directly, with no separate compile step, and bundles a package manager, test runner, and bundler into a single toolchain. CompileBytes runs Bun 1.3.10 in an isolated hosted runtime, so you can execute modern JavaScript and TypeScript, including top-level await and ES modules, without installing Bun locally.
Designed as a drop-in alternative to Node.js, Bun implements much of the Node API surface plus its own fast, Web-standard APIs such as Bun.serve and the built-in fetch. It understands TypeScript and JSX out of the box without extra configuration, and emphasizes speed across installing dependencies, running scripts, and executing tests. This makes it convenient for scripts, servers, and tooling where startup time and developer ergonomics matter.
main.ts is the entry point. Add helper files from the explorer and import them into your project.
Use the Input panel to pipe standard input to your program when it needs data.
Run sends your code to a fresh hosted runtime and streams the result into the output panel.
Your draft stays in this browser, and Share creates a separate snapshot link.
main.ts imports a typed export from helper.ts in Bun’s TypeScript mode.
import { answer } from "./helper";
console.log(answer());
export const answer = (): number => 42;
console.log("Hello, World!");function square(n) {
return n * n;
}
console.log(square(7));const nums = [1, 2, 3, 4, 5];
const squares = nums.map((x) => x * x);
console.log(squares.join(", "));function greet(name: string): string {
return `Hello, ${name}!`;
}
console.log(greet("CompileBytes"));interface User {
name: string;
age: number;
}
const users: User[] = [
{ name: "Ada", age: 36 },
{ name: "Linus", age: 54 },
];
for (const u of users) {
console.log(`${u.name} is ${u.age}`);
}async function delayed(value: string): Promise<string> {
await new Promise((r) => setTimeout(r, 10));
return value.toUpperCase();
}
const result = await delayed("hello");
console.log(result);let input = "";
for await (const chunk of Bun.stdin.stream()) {
input += Buffer.from(chunk).toString();
}
console.log(`You typed: ${input.trim()}`);function first<T>(items: T[]): T | undefined {
return items[0];
}
console.log(first([10, 20, 30]));
console.log(first(["a", "b"]));const nums = [1, 2, 3, 4, 5, 6];
const evens = nums.filter((n) => n % 2 === 0);
const total = nums.reduce((acc, n) => acc + n, 0);
console.log("evens:", evens);
console.log("total:", total);The editor uses Monaco, the engine behind VS Code, with language-aware editing tools and familiar keyboard controls.
Type or paste your code into the editor, then click Run (or press Ctrl/Cmd + Enter) to execute it.
Output streams into the console panel, including runtime errors, exit status, and execution time.
Nothing to install and no account to create — code runs in an isolated hosted runtime.
Language-aware autocomplete and IntelliSense suggestions where the editor has a matching language service
Syntax highlighting, with native compiler and runtime errors shown in the console
Bracket matching, auto-indentation, code folding, and a minimap
Multi-cursor editing plus find & replace (Ctrl/Cmd + F)
Full undo/redo history and copy to clipboard
Built on Monaco — the same editor that powers VS Code
Run on demand, or turn on Auto-run to execute on every change
Stop long-running or infinite programs at any time
A real console shows standard output, errors, exit status, and execution time
Pass standard input (stdin) to your program from the Input panel — one value per line
Switch between light and dark themes
Adjust font size and other editor settings
Toggle side-by-side or top/bottom layouts
Enter distraction-free fullscreen mode
Generate a shareable link to your exact code in one click — no login needed
Your work autosaves to your browser, so you can pick up where you left off
Copy the active file to your clipboard
Run code: Ctrl/Cmd + Enter
Find & replace: Ctrl/Cmd + F
Open the full shortcut list from the keyboard icon in the toolbar
Bun is one of 23 linked-project compilers. Run always starts main.ts; selecting a helper tab changes what you edit, not the entry file.
main.ts imports a typed export from helper.ts in Bun’s TypeScript mode.
Linked-project languages (23): Node.js, TypeScript, Deno, Python, C, Go, Dart, Swift, Rust, Ruby, PHP, Java, Kotlin, C++, C#, Nim, Crystal, Haxe, Zig, Scala, D, Bun, Objective-C.
Single-file scratchpads (46): Matplotlib, NumPy, pandas, Haskell, Clojure, Perl, Lua, Tcl, jq, Raku, Elixir, Bash, Zsh, Nushell, R, Assembly (NASM), Julia, Octave, Groovy, PowerShell, Visual Basic .NET, Odin, Pascal, Lisp, Erlang, CoffeeScript, COBOL, BASIC, V, Racket, OCaml, Prolog, AWK, Emacs Lisp, Emojicode, Forth, F#, Fortran, Assembly (NASM64), Solidity, Mojo, Ada, WASM (WAT), Gleam, Shell Script (sh), Scheme. Their extra project files are not submitted to the runtime.
Download project exports every Bun tab and a README in one ZIP archive.