Bun vs Deno 2: The Battle for the Future of JavaScript Runtimes

Node.js turned 17 in 2026 and it shows. While still dominant, its ecosystem carries decades of legacy decisions — node_modules, CommonJS/ESM friction, a bloated npm client, and no built-in TypeScript support. Two newer runtimes are challenging that dominance, each with a distinct philosophy.

Bun is a speed-first, compatibility-first runtime that aims to replace Node.js with a drop-in faster alternative. Deno 2 is a security-first, standards-first runtime that embraces web platform APIs and rethinks what a JavaScript runtime should be.

Which should you use? Let’s dig in.

Photo by Gabriel Heinzer on Unsplash

The State of Node.js in 2026

Node.js isn’t going anywhere. It powers 60%+ of server-side JavaScript production workloads. But it has structural problems that are hard to fix without breaking changes:

• TypeScript requires transpilation: Even in 2026, node --experimental-strip-types is still “experimental”
• node_modules hell: Billions of small files, nested dependency trees, phantom dependencies
• Security model: Trust-all-by-default means every npm package has full system access
• Module system confusion: CommonJS vs ESM interop remains painful
• Slow test runner: Jest, Vitest, and similar tools add build overhead

Both Bun and Deno were designed from the start to fix these problems.

Bun: Speed Above All

Bun, built by Jarred Sumner and the Oven team, launched stable in September 2023. Its core bet: raw performance plus Node.js compatibility = easy migration.

What Makes Bun Fast

Bun is written in Zig and uses JavaScriptCore (WebKit’s JS engine, also used by Safari) instead of V8. JSC tends to have faster startup times; Bun also implements native optimizations for I/O-heavy workloads.

Benchmark highlights (2026 data):

• HTTP server throughput: Bun handles ~3× more requests/sec than Node.js on http benchmarks
• npm install: Bun installs packages 10–25× faster than npm, 3–5× faster than pnpm
• Test runner: Bun’s built-in test runner is 5–10× faster than Vitest for large test suites
• Startup time: ~2ms vs Node.js ~50ms for simple scripts

Bun’s Toolchain

Bun ships as a single binary that replaces Node, npm, npx, and ts-node:

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

# Run TypeScript directly — no transpilation step
bun run server.ts

# Package management (compatible with package.json)
bun install
bun add hono @hono/node-server
bun remove express

# Run tests
bun test

# Bundle for production
bun build ./src/index.ts --outdir ./dist --target node

Node.js Compatibility

Bun implements the Node.js API surface — fs, path, http, crypto, child_process, etc. Most Node.js applications run on Bun with zero code changes. The compatibility layer covers >95% of npm packages.

# Run a Node.js app on Bun without changes
bun run server.js

# Install from npm, lock file is compatible
bun install  # reads package.json, generates bun.lockb

HTTP Server with Bun

// server.ts
const server = Bun.serve({
  port: 3000,
  async fetch(req) {
    const url = new URL(req.url);
    
    if (url.pathname === "/api/hello") {
      return Response.json({ message: "Hello from Bun!", runtime: "bun" });
    }
    
    return new Response("Not Found", { status: 404 });
  },
});

console.log(`Listening on http://localhost:${server.port}`);

bun run server.ts

No transpile step. No bundler config. TypeScript just works.

Deno 2: Standards and Security First

Deno was created by Ryan Dahl — the original creator of Node.js — as his answer to his own regrets. Deno 2, released in late 2024, made a major pivot: full npm compatibility while keeping Deno’s core principles.

Deno’s Core Principles

1. Secure by Default

Every Deno program runs in a sandbox. No filesystem, network, or environment access without explicit permission:

# Grant specific permissions
deno run --allow-net=api.example.com --allow-read=./data server.ts

# Or use a deno.json permissions config
deno run server.ts  # reads permissions from deno.json

2. Web Platform APIs

Deno implements browser-compatible APIs: fetch, Request, Response, URL, ReadableStream, Crypto, WebSocket. Code written for Deno often runs in the browser with no changes.

3. TypeScript Native

TypeScript runs natively in Deno — no tsconfig.json, no transpilation step.

4. npm Compatibility (Deno 2)

The major Deno 2 change: full npm package support via the npm: specifier:

import express from "npm:express@4";
import { Hono } from "npm:hono";
import _ from "npm:lodash";

No node_modules directory. Deno downloads packages to a global cache.

Deno’s Toolchain

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

# Run with permissions
deno run --allow-net server.ts

# Format (like gofmt — opinionated, non-configurable)
deno fmt

# Lint
deno lint

# Test
deno test

# Compile to standalone binary
deno compile --allow-net server.ts -o server

# Serve (Deno Deploy-compatible runtime)
deno serve server.ts

HTTP Server with Deno

// server.ts
import { Hono } from "npm:hono";

const app = new Hono();

app.get("/api/hello", (c) => {
  return c.json({ message: "Hello from Deno 2!", runtime: "deno" });
});

app.get("/api/secure-data", async (c) => {
  // Deno enforces that --allow-env was passed; crashes otherwise
  const apiKey = Deno.env.get("API_KEY");
  return c.json({ key: apiKey?.slice(0, 4) + "..." });
});

Deno.serve({ port: 3000 }, app.fetch);

deno run --allow-net --allow-env server.ts

Head-to-Head Comparison

Performance

Bun wins on raw speed. Deno is meaningfully faster than Node.js but not as aggressive as Bun.

Developer Experience

Ecosystem Maturity

Node.js still wins on ecosystem breadth. But both Bun and Deno support npm packages now, which narrows the gap significantly. The main remaining gaps are native addons (.node binaries) — neither runtime supports them as well as Node.js.

When to Use Each

Choose Bun when:

• You want to speed up an existing Node.js project with minimal effort
• Build performance (install time, test time) is a bottleneck
• You have a large npm dependency tree you can’t easily change
• Your team is Node.js-centric and wants familiar tooling

Choose Deno when:

• Security is a priority (sandboxed execution, explicit permissions)
• You’re building edge-deployed functions (Deno Deploy, Cloudflare Workers-compatible)
• You want strict web standards compliance
• You value opinionated tooling (fmt, lint, test) with zero config
• You’re building a new project and want a clean, modern foundation

Stay on Node.js when:

• You rely on native addons (.node modules)
• Your team has deep Node.js expertise and no migration appetite
• You’re in a compliance-sensitive environment where runtime maturity matters
• The stability guarantees of a 17-year-old runtime matter more than performance

Migration Guide: Node.js → Bun

For most Express or Fastify apps:

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

# 2. Replace npm with bun (generates bun.lockb)
bun install

# 3. Replace npm start / node server.js
bun run server.ts

# 4. Run tests
bun test

For 80% of Node.js projects, that’s it. The main failure points are native addons and obscure Node.js APIs — check npmjs.com/package/bun-plugin-node-polyfills for polyfill support.

The Real Question: Deployment

Runtime choice affects deployment strategy:

• Bun: Deploy like Node.js. Docker images with oven/bun base. Platforms like Railway, Fly.io, and Render support Bun natively.
• Deno: Deploy to Deno Deploy (their global edge platform) or self-host. Docker with denoland/deno. Deno runs on Cloudflare Workers (via compatibility layer).
• Node.js: Every cloud platform supports it. Maximum deployment flexibility.

Conclusion

In 2026, the JavaScript runtime landscape is genuinely multi-runtime. Bun has made it trivially easy to get 2–3× performance improvements with minimal migration cost. Deno 2’s npm compatibility removed the biggest adoption barrier, and its security model is compelling for production workloads.

The winner? Use Bun when speed matters. Use Deno when security and standards matter. Use Node.js when you need maximum ecosystem coverage.

The future of server-side JavaScript isn’t Node.js vs everything else — it’s a healthy ecosystem where the right runtime matches the right workload. And that’s a good thing.

Photo by JJ Ying on Unsplash

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