Bun vs Node.js: A Practical Comparison for Backend Engineers

Bun is fast. The benchmarks are impressive. But benchmarks test synthetic scenarios—let’s look at what matters when you’re shipping production APIs.

Startup Time

Bun genuinely wins here. Cold starts matter for serverless:

# Node.js
$ time node -e "console.log('hi')"
real    0m0.035s

# Bun
$ time bun -e "console.log('hi')"
real    0m0.007s

5x faster. For a Lambda function that initializes an Express app with middleware, the difference is more dramatic: ~150ms vs ~40ms.

Package Installation

# Node.js (npm)
$ time npm install
real    0m8.432s

# Bun
$ time bun install
real    0m1.203s

Bun’s package manager is legitimately fast. It resolves dependencies differently and uses a global cache aggressively.

TypeScript Support

Bun runs .ts files directly. No ts-node, no tsx, no compilation step:

bun run src/server.ts

This is genuinely nice for development. Node.js now has --experimental-strip-types in v22+, but it strips types��no enum, no namespace, no decorator metadata.

HTTP Server Performance

Here’s where the nuance matters. Raw “hello world” benchmarks:

Bun.serve:  ~120,000 req/s
Node http:  ~45,000 req/s
Fastify:    ~55,000 req/s
Express:    ~15,000 req/s

But a real API endpoint does: JSON parsing → validation → auth check �� database query → serialization. The HTTP layer is rarely the bottleneck. A typical endpoint:

Bun + Elysia:     ~8,000 req/s
Node + Fastify:   ~7,200 req/s

The gap shrinks to ~10% once real work is involved.

The Ecosystem Question

This is where Node.js still dominates:

Feature	Node.js	Bun
Native node_modules	✅ Full	✅ Good
npm packages	✅ 2M+	⚠️ Most work
Native addons (C++)	✅ Full	⚠️ Partial
node: built-in modules	✅ Full	⚠️ ~90%
AWS SDK	✅ Full	⚠️ Works
Prisma	✅ Full	✅ Works
Sharp (image processing)	✅ Full	⚠️ Issues

The “most work” is the problem. When a package doesn’t work in Bun, you’re debugging runtime compatibility instead of building features.

Built-in Test Runner

Both have built-in test runners now. Bun’s is compatible with Jest’s API:

// Works in both
import { describe, it, expect } from "bun:test"; // Bun
import { describe, it } from "node:test";         // Node

describe("math", () => {
  it("adds", () => {
    expect(1 + 1).toBe(2);
  });
});

SQLite Built-in

Bun includes SQLite natively. For embedded databases, caching, or queue systems:

import { Database } from "bun:sqlite";
const db = new Database("app.db");
db.run("CREATE TABLE IF NOT EXISTS kv (key TEXT PRIMARY KEY, value TEXT)");

Node.js now has this too with node:sqlite (experimental in v22).

My Recommendation

Use Bun for:

• Local development (fast startup, native TS)
• Scripts and tooling (bun run, bun install)
• Serverless functions where cold start matters
• New projects where you control the full stack

Stick with Node.js for:

• Existing production systems
• Projects relying on native addons
• When you need the full npm ecosystem guaranteed
• Enterprise environments requiring LTS stability

The pragmatic approach: Use bun install and bun run locally for speed, but deploy on Node.js for stability. Best of both worlds.