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bun-runtime

Skill0 starsChanged 4 months agoMITView on GitHub

Bun as runtime, package manager, bundler, and test runner. When to choose Bun vs Node, migration notes, and Vercel support.

  • Reads credentials

We split this skill into the rules it gives an agent

4 rules. 2 are common, 0 are distinctive, and 2 are very specific to this project.

  • 2

    Common

    Most of the 25 edited versions we read keep these.

  • 0

    Distinctive

    This author's own choices. Worth a look.

  • 2

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Common:

    Use when: adopting Bun, migrating from Node, writing or debugging Bun scripts/tests, or configuring Bun on Vercel or other platforms.

    line 17
  2. Very specific:

    Commit the lockfile (bun.lock or bun.lockb) for reproducible installs.

    line 83
  3. Very specific:

    Prefer bun run for scripts.

    line 84
  4. Common:

    Keep dependencies up to date.

    line 85

“Common” is measured: kept by at least 6 in 10 of the 25 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Bun Runtime

Bun is a fast all-in-one JavaScript runtime and toolkit: runtime, package manager, bundler, and test runner.

When to Use

  • Prefer Bun for: new JS/TS projects, scripts where install/run speed matters, Vercel deployments with Bun runtime, and when you want a single toolchain (run + install + test + build).
  • Prefer Node for: maximum ecosystem compatibility, legacy tooling that assumes Node, or when a dependency has known Bun issues.

Use when: adopting Bun, migrating from Node, writing or debugging Bun scripts/tests, or configuring Bun on Vercel or other platforms.

How It Works

  • Runtime: Drop-in Node-compatible runtime (built on JavaScriptCore, implemented in Zig).
  • Package manager: bun install is significantly faster than npm/yarn. Lockfile is bun.lock (text) by default in current Bun; older versions used bun.lockb (binary).
  • Bundler: Built-in bundler and transpiler for apps and libraries.
  • Test runner: Built-in bun test with Jest-like API.

Migration from Node: Replace node script.js with bun run script.js or bun script.js. Run bun install in place of npm install; most packages work. Use bun run for npm scripts; bun x for npx-style one-off runs. Node built-ins are supported; prefer Bun APIs where they exist for better performance.

Vercel: Set runtime to Bun in project settings. Build: bun run build or bun build ./src/index.ts --outdir=dist. Install: bun install --frozen-lockfile for reproducible deploys.

Examples

Run and install

# Install dependencies (creates/updates bun.lock or bun.lockb)
bun install

# Run a script or file
bun run dev
bun run src/index.ts
bun src/index.ts

Scripts and env

bun run --env-file=.env dev
FOO=bar bun run script.ts

Testing

bun test
bun test --watch
// test/example.test.ts
import { expect, test } from "bun:test";

test("add", () => {
  expect(1 + 2).toBe(3);
});

Runtime API

const file = Bun.file("package.json");
const json = await file.json();

Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Hello");
  },
});

Best Practices

  • Commit the lockfile (bun.lock or bun.lockb) for reproducible installs.
  • Prefer bun run for scripts. For TypeScript, Bun runs .ts natively.
  • Keep dependencies up to date; Bun and the ecosystem evolve quickly.

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