Deno 2.0 vs Bun: The Battle of Modern JavaScript Runtimes

Deno 2.0 vs Bun: A Detailed Comparison with Code Examples

With the growing number of alternatives to Node.js, Deno 2.0 and Bun have emerged as two strong contenders for modern JavaScript/TypeScript runtime environments. Both offer unique approaches to web development, emphasizing security, performance, and modern standards. In this post, we’ll dive deep into the differences between Deno 2.0 and Bun, showcasing their features, use cases, and code examples.

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Deno 2.0

Deno was created by Ryan Dahl (the original creator of Node.js) to address shortcomings in Node.js, particularly around security and module management. Deno 2.0 brings numerous improvements while staying true to its original goals of security, simplicity, and modern web standards.

Key Features

1. Security by Default: Deno restricts access to the file system, network, and environment variables unless explicitly permitted via flags.
2. Built-in TypeScript Support: TypeScript is supported out of the box, with no additional configuration needed.
3. ESM First: Deno uses native ES Modules (ESM) for module management, unlike Node.js's CommonJS (require syntax).
4. No node_modules: Deno doesn’t use node_modules or package.json. Instead, it allows direct URL imports for packages.
5. Web API Support: Deno includes many web platform APIs like fetch and WebSocket natively, aligning with browser-based standards.

Deno Example

import { serve } from "https://deno.land/std@0.207.0/http/server.ts";

const handler = (request: Request): Response => {
  return new Response("Hello from Deno!");
};

console.log("Listening on http://localhost:8000");
await serve(handler, { port: 8000 });

Deno's module imports are URL-based, which means you can import libraries directly from online repositories. This eliminates the need for package management tools like npm or yarn.

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Bun

Bun is a newer runtime for JavaScript and TypeScript, focused on speed and developer experience. Written in Zig, a low-level language, Bun aims to be the fastest JavaScript runtime available while offering built-in tools for bundling, transpiling, and more.

Key Features

1. Blazing Fast: Bun is optimized for performance, with fast script execution, dependency installation, and server response times.
2. Bundler & Transpiler: It comes with a built-in JavaScript/TypeScript bundler and transpiler, making it a one-stop solution for frontend and backend development.
3. Node.js Compatibility: Bun is compatible with most npm packages and uses node_modules, allowing easy migration from Node.js projects.
4. Fast npm Install: The bun install command is significantly faster than npm or yarn, cutting down the time spent managing dependencies.
5. Native Web APIs: Like Deno, Bun supports modern web APIs like fetch out of the box.

Bun Example

import { serve } from "bun";

serve({
  port: 8000,
  fetch(req) {
    return new Response("Hello from Bun!");
  }
});

console.log("Listening on http://localhost:8000");

Bun’s code looks similar to both Deno and Node.js, but it focuses on speed and simplicity. The built-in support for modern JavaScript standards means you don’t need additional tools like Babel or Webpack.

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Key Differences

Feature	Deno 2.0	Bun
Performance	Great, but not as fast as Bun	Ultra fast, especially for npm installs and script execution
Security	Secure by default, requires permission flags	No security sandbox, similar to Node.js
Package Management	Uses URL-based imports, no node_modules	Supports npm and node_modules
TypeScript Support	Built-in support, no config needed	Built-in support, optimized for speed
Bundler	No built-in bundler	Includes a fast bundler
Compatibility	No CommonJS, uses ESM	Mostly compatible with Node.js projects

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When to Use Deno

• Security matters: Deno’s security sandbox makes it ideal for environments where restricting file system and network access is a priority.
• You want modern standards: If you prefer using ESM, fetch, and TypeScript without extra setup, Deno has you covered.
• You want a fresh start: Deno does away with node_modules and package.json, opting for a simpler and more modern ecosystem.

Best for: Security-focused applications and developers looking for a clean, TypeScript-first environment.

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When to Use Bun

• Speed is critical: Bun is one of the fastest JavaScript runtimes, outperforming Node.js and Deno in many benchmarks.
• You need a full toolchain: Bun’s built-in bundler, transpiler, and runtime mean you don’t need to install tools like Webpack, Babel, or esbuild.
• You want compatibility with Node.js: Bun’s close compatibility with Node.js makes it easier to transition or integrate with existing Node.js projects.

Best for: Performance-driven applications and developers looking for a faster alternative to Node.js without sacrificing compatibility.

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Conclusion

Both Deno 2.0 and Bun offer exciting alternatives to Node.js, but they excel in different areas. If you prioritize security, modern standards, and a simplified developer experience, Deno might be the right choice. On the other hand, if you want sheer speed and a drop-in replacement for Node.js with built-in tooling, Bun is an excellent option.

Which runtime are you using or planning to use? Let me know in the comments!

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Further Reading:

• Deno Documentation
• Bun Documentation

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This post could be a great starting point for developers exploring these newer runtime environments. Feel free to tweak it further for your audience on Dev.to!