# Bun Detect when code is executed with Bun

> Detect when code is executed with Bun

- Skill: `jarle/bun-detect-when-code-is-executed-with-bun` (Agent Skill)
- Install (CLI): `npx skillmds@latest add jarle/bun-detect-when-code-is-executed-with-bun`
- Raw SKILL.md: https://api.skillmd.com/api/skills/jarle/bun-detect-when-code-is-executed-with-bun/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: jarle (https://skillmd.com/u/jarle)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/jarle/bun-detect-when-code-is-executed-with-bun

---


# Detect when code is executed with Bun

The recommended way to detect when code is being executed with Bun is to check `process.versions.bun`. This works in both JavaScript and TypeScript without requiring any additional type definitions.

```ts  theme={"theme":{"light":"github-light","dark":"dracula"}}
if (process.versions.bun) {
  // this code will only run when the file is run with Bun
}
```

***

Alternatively, you can check for the existence of the `Bun` global. This is similar to how you'd check for the existence of the `window` variable to detect when code is being executed in a browser.

<Note>
  This approach will result in a type error in TypeScript unless `@types/bun` is installed. You can install it with `bun
    add -d @types/bun`.
</Note>

```ts  theme={"theme":{"light":"github-light","dark":"dracula"}}
if (typeof Bun !== "undefined") {
  // this code will only run when the file is run with Bun
}
```