Bun and TypeScript Development Standards

This skill guides TypeScript development using Bun as the exclusive runtime and package manager.

Core Principles

Use Bun exclusively - No Node.js, npm, yarn, or pnpm TypeScript only - No JavaScript (except Nx generators)
Strict mode enabled - All code compiles with strict: true 1 function per module MAX - Each module exports exactly one primary function Always arrow functions - Use arrow functions instead of named functions or classes Barrel modules - Use index.ts for public API re-exports Test collocation - Tests next to implementation as .test.ts Explicit types - No any, explicit return types required

Module System Strategy

•Root workspace: CommonJS (no "type": "module" in root package.json)
•Apps & Packages: ESM ("type": "module" in package.json)
•Nx Executors/Generators: CommonJS (Nx convention in tools/)
•Test Files: Bun tests use ESM, Jest uses CommonJS

Bun Commands

bash

# Package management
bun install
bun add <package>
bun add -D <dev-package>
bun remove <package>

# Running TypeScript
bun run src/index.ts
bun --watch src/index.ts
bun test

# Building with Nx
bun run build
bunx nx build <package>
bunx nx build <package> --watch

TypeScript Configuration

json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ESNext",
    "moduleResolution": "node",
    "declaration": true,
    "sourceMap": true,
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "resolveJsonModule": true
  }
}

Code Organization

One Function Per Module MAX

typescript

// ✅ Good: Arrow function, single export
export const validateName = (name: string): boolean => {
  return /^[a-z][a-z0-9-]*$/.test(name);
};

// ❌ Bad: Named function declaration
export function validateName(name: string): boolean {
  return /^[a-z][a-z0-9-]*$/.test(name);
}

// ❌ Bad: Multiple unrelated functions in one file
// ❌ Bad: Class-based implementation

Barrel Modules

typescript

// src/utils/index.ts
export { validateName } from "./validate-name";
export { formatError } from "./format-error";

// Consumers use clean imports
import { validateName } from "./utils";

Unit Test Collocation

Tests must be colocated with implementation files as .test.ts:

typescript

// src/utils/validate-name.ts - Implementation
// src/utils/validate-name.test.ts - Test (same directory)

import { describe, it, expect } from "bun:test";
import { validateName } from "./validate-name";

describe("validateName", () => {
  it("should validate names", () => {
    expect(validateName("my-plugin")).toBe(true);
  });
});

Linting with Biome

bash

# Lint and format
bun run lint
bun run lint:affected
bun run format
bun run format:check
bun run validate:tsdoc

# Manual Biome usage
biome check --write .
biome format --write .
biome check src/utils/validate.ts
biome explain noUnusedVariables
biome rage

Biome configuration in biome.json:

•Line width: 120
•Indent width: 2
•Complexity rules enabled
•TSDoc validation integrated

Bun Features

Shell

typescript

import { $ } from "bun";
const output = await $`ls -la`.text();

File I/O

typescript

const file = Bun.file("package.json");
const json = await file.json();
await Bun.write("output.txt", "content");

Build Setup

json

{
  "name": "@scope/package",
  "main": "dist/index.cjs",
  "module": "dist/index.js",
  "types": "dist/index.d.ts",
  "files": ["dist"],
  "scripts": {
    "build": "bunx tsup src/index.ts --format esm,cjs --dts --out-dir dist",
    "test": "bun test",
    "dev": "bunx tsup src/index.ts --format esm,cjs --dts --out-dir dist --watch"
  }
}

Troubleshooting

bash

# Bun issues
bun upgrade
rm -rf ~/.bun/install/cache
rm -rf node_modules bun.lockb && bun install

# TypeScript issues
bunx tsc --showConfig
bunx tsc --noEmit
rm -rf dist && bun run build

# Nx cache issues
bunx nx reset
bunx nx reset && rm -rf node_modules bun.lockb && bun install

File Naming

typescript

// ✅ Correct
src/index.ts
src/utils/validate-name.ts
src/utils/validate-name.test.ts

// ❌ Incorrect
src/index.js // No JavaScript
src/Plugin.ts // Use kebab-case
src/utils/helpers.ts // Too generic

Type Patterns

typescript

// Prefer types for functions and unions
export type Validator = (value: unknown) => boolean;
export type Status = "pending" | "success" | "error";

// Use interfaces for object shapes
export interface Config {
  name: string;
  version: string;
}