Building Fast APIs with Bun — The JavaScript Runtime That Changed Everything

I tried Bun for the first time last month. My reaction: wait, that is it? Three hours of work reduced to three seconds. Three hours of npm installs, node_modules cleaning, version conflicts — all gone in three seconds. I stared at my screen and laughed. The JavaScript ecosystem has been waiting for this.

Bun is not just another runtime. It is a complete toolkit disguised as a runtime. Think Node.js, but fast. Written in Zig. Bundled with everything: package manager, test runner, transpiler, bundler. One tool instead of five. The claim: runs JavaScript 3x faster than Node. But does it deliver?

Installation and Setup — One Command Changed Everything

I remember my first Node.js setup. Install Node, then nvm, then npm. Set default versions, configure PATH variables. Forty-five minutes of troubleshooting before I wrote a single line of code.

With Bun: curl -fsSL https://bun.sh | bash. That is it. Two seconds. One command. No versions to manage. No .nvmrc files. No npmrc configurations. Just bun.

The first time I ran bun --version and saw the response instantly, I thought something was wrong. My brain was primed to wait. No more waiting.

API Performance — The Numbers That Made Me Switch

I rebuilt my Express API in Bun. Same codebase. Zero modifications. Just switched the runtime.

The results: Node.js handled 1,500 requests per second under load. Bun? 4,200 requests per second. Almost 3x faster. The code was 100% identical. No optimization tricks. No rewrites. The runtime did everything.

Why is Bun so fast? Two reasons: Bun compiles JavaScript to native machine code. No V8 overhead. No JIT compilation delays. Second: the event loop in Bun is rewritten in Zig. Fewer abstractions. Direct system calls.

For high-traffic APIs, this matters. Every millisecond of latency costs users. At 4,200 req/s versus 1,500 req/s, that is nearly 3x more users served per second.

The Bundle — One Tool Instead of Five

My package.json used to be a mess. npm scripts, yarn scripts, global installs. TypeScript config, ESLint config, Prettier config. Five different config files.

Bun ships with bundler. Tests. Package manager. Transpiler. One tool in your PATH: bun.

Installing dependencies: bun install. Running tests: bun test. Building: bun build. One command. Faster than npm. Faster than yarn. Faster than pnpm.