bun install              # Install all dependencies
bun install --frozen-lockfile  # CI/CD lockfile validation
bun add <pkg>            # Add dependency
bun add -d <pkg>         # Add devDependency
bun remove <pkg>         # Remove dependency
bun update               # Update outdated packages
bun ci                   # CI-optimized install (--frozen-lockfile)
bunx <pkg>               # Execute package without installing (100x faster than npx)

{
  "workspaces": ["packages/*", "apps/*"],
  "dependencies": {
    "shared-pkg": "workspace:*"
  }
}

bun pm trust <pkg>       # Allow lifecycle scripts
bun pm untrusted         # View blocked scripts
bun why <pkg>            # Explain why package installed
bun outdated             # Show outdated packages
bun audit                # Security vulnerability check
bun patch <pkg>          # Prepare package for patching
bun link                 # Link local packages

import { describe, test, expect, beforeAll, afterEach, mock, spyOn } from "bun:test";

describe("feature", () => {
  beforeAll(() => { /* setup */ });
  afterEach(() => { mock.restore(); });

  test("basic assertion", () => {
    expect(2 + 2).toBe(4);
  });

  test("async operation", async () => {
    const result = await fetchData();
    expect(result).toMatchObject({ status: "ok" });
  });

  test.each([[1, 2, 3], [2, 3, 5]])("adds %i + %i = %i", (a, b, expected) => {
    expect(a + b).toBe(expected);
  });
});

import { mock, spyOn } from "bun:test";

const mockFn = mock(() => 42);
mockFn.mockImplementation(() => 100);
mockFn.mockReturnValue(200);

const spy = spyOn(object, "method");
spy.mockResolvedValue({ data: "test" });

// Module mocking
mock.module("./api", () => ({
  fetchUser: mock(() => ({ id: 1, name: "Test" }))
}));

bun test                 # Run all tests
bun test --watch         # Watch mode
bun test --coverage      # Enable coverage
bun test -t "pattern"    # Filter by test name
bun test --timeout=5000  # Set timeout
bun test --bail          # Stop on first failure
bun test --update-snapshots  # Update snapshots

const result = await Bun.build({
  entrypoints: ["./src/index.tsx"],
  outdir: "./dist",
  target: "browser",  // "browser" | "bun" | "node"
  format: "esm",      // "esm" | "cjs" | "iife"
  minify: true,
  sourcemap: "external",
  splitting: true,    // Code splitting
  external: ["react", "react-dom"],
  define: {
    "process.env.NODE_ENV": '"production"'
  },
  loader: {
    ".png": "dataurl",
    ".svg": "text"
  },
  plugins: [myPlugin],
  naming: {
    entry: "[dir]/[name].[ext]",
    chunk: "[name]-[hash].[ext]"
  }
});

if (!result.success) {
  console.error(result.logs);
}

bun build ./src/index.tsx --outdir ./dist --minify --sourcemap=external
bun build ./src/index.ts --compile --outfile myapp  # Single executable

const myPlugin: BunPlugin = {
  name: "yaml-loader",
  setup(build) {
    build.onLoad({ filter: /\.yaml$/ }, async (args) => {
      const text = await Bun.file(args.path).text();
      return {
        contents: `export default ${JSON.stringify(YAML.parse(text))}`,
        loader: "js"
      };
    });
  }
};

bun run index.ts      # Just works
bun run index.tsx     # JSX supported

{
  "compilerOptions": {
    "lib": ["ESNext"],
    "target": "ESNext",
    "module": "ESNext",
    "moduleDetection": "force",
    "moduleResolution": "bundler",
    "allowImportingTsExtensions": true,
    "verbatimModuleSyntax": true,
    "noEmit": true,
    "strict": true,
    "skipLibCheck": true,
    "types": ["bun-types"]
  }
}

bunx tsc --noEmit

undefined

---

undefined

3. **Update scripts in package.json:**
```json
{
  "scripts": {
    "dev": "bun run --watch src/index.ts",
    "test": "bun test",
    "build": "bun build src/index.ts --outdir dist"
  }
}

bun add -d @types/bun

undefined

{
  "main": "src/index.ts"  // Not "build/index.js"
}

// Use Bun's native APIs for I/O
const file = Bun.file("large.txt");  // Zero-copy
const content = await file.text();
await Bun.write("output.txt", processedData);

// Use Promise.all for concurrent operations
const [users, posts] = await Promise.all([
  db.query("SELECT * FROM users"),
  db.query("SELECT * FROM posts")
]);

// Use Bun.serve() static routes
Bun.serve({
  static: {
    "/": homepage,
    "/about": aboutPage
  },
  fetch(req) { /* dynamic routes */ }
});

// Use bun:sqlite for local data
import { Database } from "bun:sqlite";
const db = new Database(":memory:");
const stmt = db.prepare("SELECT * FROM users WHERE id = ?");

// HTTP server error handling
Bun.serve({
  fetch(req) {
    try {
      return handleRequest(req);
    } catch (error) {
      console.error(error);
      return new Response("Internal Error", { status: 500 });
    }
  },
  error(error) {
    return new Response(`Error: ${error.message}`, { status: 500 });
  }
});

// Process-level error handling
process.on("uncaughtException", (error) => {
  console.error("Uncaught:", error);
  process.exit(1);
});

my-bun-project/
├── src/
│   ├── index.ts        # Entry point
│   ├── server.ts       # HTTP server
│   └── lib/            # Utilities
├── test/
│   └── *.test.ts       # Test files
├── bunfig.toml         # Bun configuration
├── tsconfig.json       # TypeScript config
├── package.json
└── .env.local          # Local secrets (gitignored)

bun --inspect server.ts         # Start debugger
bun --inspect-brk server.ts     # Break at first line
bun --inspect-wait server.ts    # Wait for connection

BUN_CONFIG_VERBOSE_FETCH=curl bun run server.ts

Bun.serve({
  port: 3000,
  fetch(req, server) {
    if (server.upgrade(req)) return;
    return new Response("Hello Bun!");
  },
  websocket: {
    open(ws) { console.log("Connected"); },
    message(ws, message) { ws.send(`Echo: ${message}`); },
    close(ws) { console.log("Disconnected"); }
  }
});

Bun.serve({
  async fetch(req) {
    const path = new URL(req.url).pathname;
    const file = Bun.file(`./public${path}`);
    if (await file.exists()) {
      return new Response(file);
    }
    return new Response("Not Found", { status: 404 });
  }
});

import { Database } from "bun:sqlite";

const db = new Database("app.db");
db.run(`CREATE TABLE IF NOT EXISTS users (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  name TEXT NOT NULL,
  email TEXT UNIQUE
)`);

const insert = db.prepare("INSERT INTO users (name, email) VALUES (?, ?)");
const getAll = db.prepare("SELECT * FROM users");

insert.run("Alice", "alice@example.com");
const users = getAll.all();