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Posted on • Originally published at jessinvestment.com

Bun: The All-in-One Tool That Replaces Node and npm

#node #bunjs #npm #javascript

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Bun: The All-in-One Tool That Replaces Node and npm

To run a single JavaScript project, you typically execute it with Node.js, install packages with npm, run tests with Jest, and bundle with webpack or esbuild. Bun ties all four together into a single executable. Here's what it replaces, how to install it and get started, and the limits worth knowing before you adopt it — all based on the official docs.

Four tools folded into one binary

Bun is an all-in-one toolkit for building JavaScript and TypeScript apps. The core idea is that a single command — bun — handles the role of four separate tools. The official docs state that Bun ships as a single dependency-free binary that includes a runtime, a package manager, a test runner, and a bundler.

Here's how far a single Bun install covers the environment you used to piece together from several tools.

Role Tool you used before Bun command
Runtime (running code) Node.js bun run
Package manager npm / yarn / pnpm bun install
Test runner Jest / Vitest bun test
Bundler webpack / esbuild bun build
Package execution npx bunx

Bun's pitch is that you have to manage fewer separate config files and compatibility issues per tool. The docs explain it's designed to work in existing Node.js projects without major changes.

The engine is JavaScriptCore, not V8

A key distinction for understanding Bun is the engine. Node.js runs on Google's V8 engine, but Bun runs on the JavaScriptCore engine that Apple built for Safari. And Bun itself is written in a language called Zig.

This choice isn't just a matter of taste — it affects behavior too. For example, some web-standard APIs like Headers and URL use Safari's implementation directly. Web-standard APIs like fetch, WebSocket, and ReadableStream are also built in, so code you'd use in the browser can be used on the server in much the same way.

On speed, the official docs cite two specific figures. Process startup is currently about 4x faster than Node.js, and package installation is up to 30x faster than npm. Keep in mind these are benchmark numbers that can vary depending on your environment and project.

From install to first run

Because Bun is a single binary, installation is simple. On macOS and Linux you can grab it with a one-line official install script, and other paths — Windows, installing via npm, and more — are laid out on the official installation page.

# Install on macOS / Linux
curl -fsSL https://bun.sh/install | bash

# Verify the install
bun --version

# Run TypeScript and JSX files directly, no extra config
bun run index.tsx
Enter fullscreen mode Exit fullscreen mode

The line to note is the last one. You can run .ts, .tsx, and .jsx files directly with no separate transpile config. Bun's transpiler converts these files to plain JavaScript right before execution. That cuts out the ts-node or extra build step you used to add just to use TypeScript.

Commands you'll reach for often

bun run — run scripts and files

Runs a file directly or executes a script defined in package.json. bun run start runs the start script, and bun run index.ts runs the file directly. The docs describe this execution overhead as nearly nonexistent.

bun install — install packages

Supports a global cache, workspaces, dependency overrides, and an audit feature. It reads your existing package.json as-is, so you can drop into an npm-managed project and just run bun install.

bun test — run tests

A Jest-compatible test runner is built in. It supports snapshots, DOM testing, and watch mode, and treats TypeScript as a first-class citizen. You can run tests with just bun test without installing a separate test framework.

bun build — bundling

Bundles JS, TS, and JSX targeting both browser and server. It supports features like code splitting, plugins, and HTML imports, and can handle CSS too.

bunx — run a package once

The counterpart to npx, it runs a package you haven't installed on the fly. You use it like bunx cowsay 'Hello, world!'.

What to know before adopting it

It's too early to declare that Bun instantly replaces every environment. Here are the limits the official docs mention directly, along with what to check before adopting it.

  • Full Node.js compatibility is in progress — the docs aim for compatibility with Node.js built-in globals (process, Buffer) and modules (path, fs, http, etc.), but state this is "an ongoing effort that is not yet complete." You have to check the compatibility status on a separate compatibility page.
  • Projects that depend on specific Node modules — because of that compatibility gap, a library using a module that isn't yet supported may not work as-is. For existing projects, it's safer to check compatibility status before moving over.
  • ESM recommended, CommonJS supported — Bun recommends ES modules but also supports the countless CommonJS packages still on npm. It's worth verifying behavior in advance in an environment where the two module systems are mixed.
  • Benchmark numbers are conditional — figures like 4x and 30x are values the official docs cite, but they vary with project makeup and environment. The accurate way to gauge the real impact is to measure it in your own project.

Who it's for

If you're starting a new JavaScript or TypeScript project and want to cut the burden of configuring a runtime, package manager, tests, and bundler from scratch, Bun is a candidate. It's also worth trying if you want to run TypeScript directly with no separate build config, or if install speed is your bottleneck.

Conversely, if you already have a stable Node.js production environment that depends deeply on specific Node modules, rather than a full switch it's more sensible to apply it to a small scope first — a side project or script execution — and check compatibility. After installing, running bun install and bun run in an existing project is the fastest way to get a feel for it.

Install note: macOS and Linux install with the single line curl -fsSL https://bun.sh/install | bash. Other install methods — Windows, npm, Docker, etc. — and supported platforms are covered on the official installation page. Before applying it to an existing Node project, we recommend checking compatibility status on the runtime/nodejs-compat page first.

References

This is not a hands-on review but an objective introduction based on the official docs. Feature names and figures follow the official documentation at the time of writing and may change with version and environment.

Canonical: https://jessinvestment.com/bun-the-all-in-one-tool-that-replaces-node-and-npm/

Original with full infographics and visual structure: https://jessinvestment.com/bun-the-all-in-one-tool-that-replaces-node-and-npm/

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