Getting Started with Bun: A Blazing Fast Runtime for JavaScript

by Hexagon, 3 minutes read bun javascript performance

In the ever-evolving world of JavaScript runtimes, Bun is emerging as a promising star. It might not have the maturity of Deno or Node.js, but it compensates with promising great performance. Let's explore Bun in detail.

Why Bun?

Built for performance

Bun's primary draw is its sheer speed. Designed with performance optimization at its core, it offers execution times that can give even the most established runtimes a run for their money.

Keeping It Lean

Bun takes a minimalistic approach. Without the frills and complexities, it offers a focused runtime environment. This can be especially beneficial for applications where performance is critical, and you don't want overheads.

Growing Ecosystem

While Bun might be newer compared to its counterparts, it's backed by a growing community and an expanding ecosystem of tools and packages. It is also designed to be compatible with Node.js, inheriting much of this more mature ecosystem.

A Step Towards Modern JavaScript

Being a fresh entry, Bun has the advantage of addressing some modern JavaScript needs from the ground up, providing an environment tailored for current development practices. As an example, it has built in support for TypeScript, and a built in bundler.

For an in-depth comparison on how Bun stacks up against other runtimes, see my articles: Deno vs. Bun vs. Node.js: A Feature Comparison and Deno vs. Bun vs. Node.js: A Speed Comparison.

How to Install

Setting up Bun is straightforward:

Using Shell (macOS, Linux and WSL):

curl -fsSL | bash

For more detailed installation instructions, refer to the official documentation.

Hello Bun!

Kickstart your Bun journey with a simple application. Create a new .js (or .ts) file:

console.log("Hello, Bun!");

Execute your program using bun run hello.js. You should witness the output "Hello, Bun!"

For those unfamiliar with JavaScript or looking for a refresher, I recommend the The Guide to JavaScript.

Importing Packages

Bun is compatible with the npm package registry; in fact it can install packages from npm on its own, and it's quicker than using the npm command:

bun install croner

... and the script:

import { Cron } from "croner";

const job = Cron("*/5 * * * * *", () => {
  console.log("This action will repeat every fifth second");

Built-in Test Runner

One of the notable features of Bun is its integrated test runner. This provides developers with the tools needed to ensure the reliability and stability of their applications without relying on external tools or libraries.

Here's how you can get started:

  1. Write your test in a .test.js or .test.ts file. For instance, example.test.js:
import { beforeAll, describe, expect, test } from "bun:test";

beforeAll(() => {
  // setup tests

describe("math", () => {
  test("addition", () => {
    expect(2 + 2).toBe(4);
    expect(7 + 13).toMatchSnapshot();
  1. Run the test using the bun test command, which will automatically pick up the test:
bun test

Bun will execute the tests and provide a fairly standard report, showcasing passed tests, failed tests, and execution time.

To dive deeper into testing with Bun and best practices, check the official testing documentation.

TypeScript Support in Bun Compared to Node.js

Bun, much like Deno, offers out-of-the-box support for TypeScript. This presents a refreshing change, especially for developers who are used to the more modular approach of Node.js. In Bun, there's no need for external tools like Babel or ts-node. Instead, Bun ensures that developers can seamlessly leverage the advantages of static typing and modern JavaScript features right from the get-go.

Here's how to get TypeScript up and running in your Bun project:

1. Install TypeScript Definitions for Bun's APIs: Simply run bun add -d bun-types to add it as a dev dependency.

2. Update Your tsconfig.json: Include "bun-types" in the compilerOptions.types:

  "compilerOptions": {
    "types": ["bun-types"]

3. Use Bun Globals without Issues: You can now reference Bun-specific globals like console.log(Bun.version); without any TypeScript errors.

4. Recommended Compiler Options: Bun provides a set of recommended compiler options tailored for its environment. This includes settings that enable modern features like top-level await, JSX, and .ts imports. Initializing a Bun project with bun init auto-generates this configuration for you.

Bun Resources


With its combination of raw performance, growing ecosystem, and developer-friendly features like the built-in test runner, Bun is rapidly carving a niche for itself. Whether you're starting a new project or considering a switch, Bun's unique offerings make it a worthy contender in the JavaScript runtime arena.

Unshackling JavaScript: Vanilla JS Over Shims Deno vs. Bun vs. Node.js: A Speed Comparison