Why Bun Is My New Default JavaScript Runtime

After months of experimentation, I've made Bun my default JavaScript runtime for new projects. Here's why you should consider doing the same.

What Is Bun?

Bun is an all-in-one JavaScript runtime that combines a runtime, bundler, transpiler, and package manager into a single fast tool. Built with Zig and using JavaScriptCore (Safari's engine) instead of V8, it's designed from the ground up for speed.

The Speed Difference Is Real

Let me show you the numbers from my real projects:

bash
# Installing dependencies (medium Next.js project)
npm install:  42.3s
bun install:   4.2s  # 10x faster

# Running tests (100 unit tests)
jest:         8.4s
bun test:     1.1s   # 7x faster

# Starting dev server
node:         1.2s
bun:          0.3s   # 4x faster

These aren't cherry-picked benchmarks - this is my daily experience across multiple projects.

What I Use Bun For

1. Package Management

Bun's package manager is npm-compatible but dramatically faster:

bash
# Switch to bun for any project
bun install

# Add dependencies
bun add zod drizzle-orm

# Run scripts
bun run dev

The lockfile (bun.lockb) is binary and much faster to parse than package-lock.json.

2. Running TypeScript Directly

No more ts-node or compilation step:

bash
# Just run TypeScript files directly
bun run scripts/migrate.ts
bun run src/index.ts

Bun has native TypeScript support with no configuration needed.

3. Testing

Bun's built-in test runner is Jest-compatible but faster:

typescript
// math.test.ts
import { expect, test, describe } from "bun:test";

describe("math", () => {
  test("adds numbers", () => {
    expect(2 + 2).toBe(4);
  });
});

bash
bun test

4. Building and Bundling

Bun includes a bundler that's faster than esbuild:

bash
bun build ./src/index.ts --outdir ./dist --target node

When I Still Use Node.js

Bun isn't perfect for everything yet:

• Production servers with specific Node.js APIs - Some edge cases exist
• Projects with native modules that don't have Bun support
• When the team isn't ready - Stick with what works

Getting Started

bash
# Install Bun
curl -fsSL https://bun.sh/install | bash

# Create a new project
bun init

# Or migrate an existing project
cd my-project && bun install

My Recommendation

Start using Bun for:

1. Local development - The speed improvement is immediately noticeable
2. Scripts and tooling - Run TypeScript directly, no config needed
3. New side projects - Perfect for experimenting

The JavaScript ecosystem finally has real competition in the runtime space, and developers are the winners.

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Bun has matured significantly in 2025. If you tried it a year ago and had issues, it's worth another look.