Detect when code is executed with Bun

Check process.versions.bun to detect whether code is running in Bun. This works in both JavaScript and TypeScript without extra type definitions.

if (process.versions.bun) {
  // this code will only run when the file is run with Bun
}

Alternatively, check for the Bun global, the same way you’d check for window to detect a browser.

In TypeScript, this check is a type error unless @types/bun is installed. Install it with bun add -d @types/bun. If you’re using TypeScript 6.0 or later, you also need "types": ["bun"] in your compilerOptions. See TypeScript 6 and 7 for details.

if (typeof Bun !== "undefined") {
  // this code will only run when the file is run with Bun
}