File types – Runtime

TypeScript

Bun natively supports TypeScript out of the box. All files are transpiled on the fly by Bun's fast native transpiler before being executed. Similar to other build tools, Bun does not perform typechecking; it simply removes type annotations from the file.

bun index.js
bun index.jsx
bun index.ts
bun index.tsx

Some aspects of Bun's runtime behavior are affected by the contents of your tsconfig.json file. Refer to Runtime > TypeScript page for details.

JSX

Bun supports .jsx and .tsx files out of the box. Bun's internal transpiler converts JSX syntax into vanilla JavaScript before execution.

react.tsx
function Component(props: {message: string}) {
  return (
    <body>
      <h1 style={{color: 'red'}}>{props.message}</h1>
    </body>
  );
}

console.log(<Component message="Hello world!" />);

Bun implements special logging for JSX to make debugging easier.

bun run react.tsx
<Component message="Hello world!" />

Text files

Text files can be imported as strings.

index.ts

text.txt

index.ts
import text from "./text.txt";
console.log(text);
// => "Hello world!"

text.txt
Hello world!

JSON and TOML

JSON and TOML files can be directly imported from a source file. The contents will be loaded and returned as a JavaScript object.

import pkg from "./package.json";
import data from "./data.toml";

WASI

🚧 Experimental

Bun has experimental support for WASI, the WebAssembly System Interface. To run a .wasm binary with Bun:

bun ./my-wasm-app.wasm
# if the filename doesn't end with ".wasm"
bun run ./my-wasm-app.whatever

Note — WASI support is based on wasi-js. Currently, it only supports WASI binaries that use the wasi_snapshot_preview1 or wasi_unstable APIs. Bun's implementation is not fully optimized for performance; this will become more of a priority as WASM grows in popularity.

SQLite

You can import sqlite databases directly into your code. Bun will automatically load the database and return a Database object.

import db from "./my.db" with { type: "sqlite" };
console.log(db.query("select * from users LIMIT 1").get());

This uses bun:sqlite.

Custom loaders

Support for additional file types can be implemented with plugins. Refer to Runtime > Plugins for full documentation.