bun-runtime

Name: bun-runtime
Author: affaan-m

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

INSTALLATION

npx skills add https://github.com/affaan-m/everything-claude-code --skill bun-runtime

Run in your project or agent environment. Adjust flags if your CLI version differs.

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.