Bun.js vs Deno.js

Introduction

In the evolving JavaScript landscape, modern runtimes are gaining attention as developers seek speed, security, and better tooling. Bun.js and Deno.js are two powerful alternatives to Node.js.

While both aim to improve the developer experience, they approach the runtime challenge differently. This guide compares Bun.js vs Deno.js based on performance, features, security, and ecosystem to help you choose the best fit for your project.

What Is Bun.js?

Bun.js is a fast JavaScript runtime built using the Zig programming language. It comes bundled with a transpiler, bundler, test runner, and its own package manager.

Bun is designed to be a one-stop solution for building and running JavaScript/TypeScript apps with high performance and minimal configuration.

What Is Deno.js?

Deno.js is a secure runtime for JavaScript and TypeScript, developed by Ryan Dahl, the creator of Node.js. It addresses many of Node’s design limitations, offering modern features like ES module support, TypeScript out of the box, and built-in security controls.

Unlike Bun, Deno is written in Rust.

Installation Experience

Both Bun and Deno offer simple installation steps. Here's how you install each:

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

// Install Deno.js
curl -fsSL https://deno.land/install.sh | sh

Once installed, both can be verified using:

bun --version
deno --version

Performance Benchmarks

Bun is laser-focused on speed. Benchmarks indicate Bun executes JavaScript and TypeScript significantly faster than Deno in most cases, thanks to Zig’s low-level optimizations.

// Bun - hello world
console.time("bun");
console.log("Hello from Bun!");
console.timeEnd("bun");

// Deno - hello world
console.time("deno");
console.log("Hello from Deno!");
console.timeEnd("deno");

Execution in Bun tends to be faster, particularly in I/O-heavy or bundling scenarios.

TypeScript Support

Both runtimes support TypeScript out of the box—no extra tools required.

// Bun.js - greet.ts
const greet = (name: string) => `Hello, ${name}`;
console.log(greet("Bun Dev"));

// Deno.js - greet.ts
const greet = (name: string): string => `Hello, ${name}`;
console.log(greet("Deno Dev"));

Bun compiles TypeScript faster, but Deno provides more mature diagnostics and stricter type checks.

Security Features

Deno is built with security-first principles. It denies file, network, and environment access by default, requiring explicit permissions:

deno run --allow-net server.ts

Bun currently does not enforce such permissions, making it more flexible for development but less secure in production by default.

Built-in Tooling Comparison

Ecosystem and Module Management

Bun supports npm packages directly, allowing developers to tap into the vast npm ecosystem:

bun add express

Deno, on the other hand, relies on URL-based module imports and does not use npm by default:

import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

This approach enhances security and versioning but can feel limiting to those familiar with npm.

Developer Experience

Bun focuses on performance and simplicity. You can spin up a project and run it in seconds with minimal boilerplate. Deno offers more polished tooling, intelligent error messages, and better support for web standards.

However, the learning curve might be steeper for new developers.

When to Choose Bun or Deno

• Use Bun.js if you want blazing-fast performance, npm support, and built-in tooling for modern frontend/backend development.
• Use Deno.js if you prioritize security, prefer using web standards, and are building modern, permission-aware applications.

Conclusion

Bun.js and Deno.js are reshaping the future of JavaScript runtimes. While Bun is all about speed and ease of use with npm support, Deno is designed for security, stability, and standards compliance.

Your choice depends on your project’s priorities—whether it's raw speed, ecosystem compatibility, or secure architecture. Both are excellent tools and are actively evolving, making it an exciting time to be a JavaScript developer.