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Bun.js focuses on performance, developer experience, and compatibility with the JavaScript ecosystem.
HTTP Requests
// http.ts
export default {
port: 3000,
fetch(request: Request) {
return new Response("Hello World");
},
};
// bun ./http.ts
| Requests per second | OS | CPU | Bun version |
|---|---|---|---|
| 260,000 | macOS | Apple Silicon M1 Max | 0.0.76 |
| 160,000 | Linux | AMD Ryzen 5 3600 6-Core 2.2ghz | 0.0.76 |
{% details summary="See benchmark details" %}
Measured with http_load_test by running:
$ ./http_load_test 20 127.0.0.1 3000
{% /details %}
File System
cat clone that runs 2x faster than GNU cat for large files on Linux
// cat.js
import { resolve } from "path";
import { write, stdout, file, argv } from "bun";
const path = resolve(argv.at(-1));
await write(
// stdout is a Blob
stdout,
// file(path) returns a Blob - https://developer.mozilla.org/en-US/docs/Web/API/Blob
file(path),
);
Run this with bun cat.js /path/to/big/file.
Reading from standard input
for await (const line of console) {
// line of text from stdin
console.log(line);
}
React SSR
import { renderToReadableStream } from "react-dom/server";
const dt = new Intl.DateTimeFormat();
export default {
port: 3000,
async fetch(request: Request) {
return new Response(
await renderToReadableStream(
<html>
<head>
<title>Hello World</title>
</head>
<body>
<h1>Hello from React!</h1>
<p>The date is {dt.format(new Date())}</p>
</body>
</html>,
),
);
},
};
Write to stdout with console.write:
// no trailing newline
// works with strings and typed arrays
console.write("Hello World!");
There are some more examples in the examples folder.
PRs adding more examples are very welcome!
Fast paths for Web APIs
Bun.js has fast paths for common use cases that make Web APIs live up to the performance demands of servers and CLIs.
Bun.file(path) returns a Blob that represents a lazily-loaded file.
When you pass a file blob to Bun.write, Bun automatically uses a faster system call:
const blob = Bun.file("input.txt");
await Bun.write("output.txt", blob);
On Linux, this uses the copy_file_range syscall and on macOS, this becomes clonefile (or fcopyfile).
Bun.write also supports Response objects. It automatically converts to a Blob.
// Eventually, this will stream the response to disk but today it buffers
await Bun.write("index.html", await fetch("https://example.com"));