Bun.js focuses on performance, developer experience, and compatibility with the JavaScript ecosystem.
## HTTP Requests
```ts
// 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](https://twitter.com/jarredsumner/status/1512040623200616449) | macOS | Apple Silicon M1 Max | 0.0.76 |
| [160,000](https://twitter.com/jarredsumner/status/1511988933587976192) | Linux | AMD Ryzen 5 3600 6-Core 2.2ghz | 0.0.76 |
{% details summary="See benchmark details" %}
Measured with [`http_load_test`](https://github.com/uNetworking/uSockets/blob/master/examples/http_load_test.c) by running:
```bash
$ ./http_load_test 20 127.0.0.1 3000
```
{% /details %}
## File System
`cat` clone that runs [2x faster than GNU cat](https://twitter.com/jarredsumner/status/1511707890708586496) for large files on Linux
```js
// 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
```ts
// As of Bun v0.3.0, console is an AsyncIterable
for await (const line of console) {
// line of text from stdin
console.log(line);
}
```
## React SSR
```js
import { renderToReadableStream } from "react-dom/server";
const dt = new Intl.DateTimeFormat();
export default {
port: 3000,
async fetch(request: Request) {
return new Response(
await renderToReadableStream(
Hello World
Hello from React!
The date is {dt.format(new Date())}
,
),
);
},
};
```
Write to stdout with `console.write`:
```js
// no trailing newline
// works with strings and typed arrays
console.write("Hello World!");
```
There are some more examples in the [examples](./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`](https://developer.mozilla.org/en-US/docs/Web/API/Blob) that represents a lazily-loaded file.
When you pass a file blob to `Bun.write`, Bun automatically uses a faster system call:
```js
const blob = Bun.file("input.txt");
await Bun.write("output.txt", blob);
```
On Linux, this uses the [`copy_file_range`](https://man7.org/linux/man-pages/man2/copy_file_range.2.html) syscall and on macOS, this becomes `clonefile` (or [`fcopyfile`](https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/copyfile.3.html)).
`Bun.write` also supports [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) objects. It automatically converts to a [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob).
```js
// Eventually, this will stream the response to disk but today it buffers
await Bun.write("index.html", await fetch("https://example.com"));
```