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local-cal/.ruler/02-BUN-GUIDE.md
Dmytro Stanchiev 206f028fdf init ruler
Signed-off-by: Dmytro Stanchiev <git@dmytros.dev>
2026-04-06 20:48:07 -04:00

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## Bun Guidelines
**CRITICAL**: Do not assume you know full Bun APIs. For **ANY** Bun API you use, confirm them by using `bun-docs` MCP tools.
Default to using Bun instead of Node.js.
- Use `bun <file>` instead of `node <file>` or `ts-node <file>`
- Use `bun test` instead of `jest` or `vitest`
- Use `bun build <file.html|file.ts|file.css>` instead of `webpack` or `esbuild`
- Use `bun install` instead of `npm install` or `yarn install` or `pnpm install`
- Use `bun run <script>` instead of `npm run <script>` or `yarn run <script>` or `pnpm run <script>`
- Use `bunx <package> <command>` instead of `npx <package> <command>`
- Bun automatically loads .env, so don't use dotenv.
### APIs
- `Bun.serve()` supports WebSockets, HTTPS, and routes. Don't use `express`.
- `bun:sqlite` for SQLite. Don't use `better-sqlite3`.
- `Bun.redis` for Redis. Don't use `ioredis`.
- `Bun.sql` for Postgres. Don't use `pg` or `postgres.js`.
- `WebSocket` is built-in. Don't use `ws`.
- Prefer `Bun.file` over `node:fs`'s readFile/writeFile
- Bun.$`ls` instead of execa.
### Testing
#### Quick Start
- Run tests: `bun test`
- Write tests in `tests/` folder
#### Test Structure
- Use `describe` blocks to group related tests
- Use `test` for individual test cases
- Use `beforeEach`/`afterEach` for setup/teardown
#### Assertions
- Import: `import { test, expect, describe, beforeEach, afterEach, mock } from "bun:test";`
- Common: `expect(value).toBe(expected)`, `expect(fn).rejects.toThrow()`
- Async: `await expect(asyncFn()).resolves.toBe(expected)`
#### Mocking
- Mock functions: `mock(fn)`
- Mock globals: `global.fetch = mock(...)`
- Restore mocks in `afterEach` or `finally`
#### Best Practices
- Mock external APIs (fetch, file I/O)
- Test error cases and edge conditions
- Use descriptive test names
- Clean up resources in `afterEach`
For more information, read the Bun API docs in `node_modules/bun-types/docs/**.mdx`.