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HK Lee
HK Lee

Posted on • Originally published at pockit.tools

Deno 2 vs Node.js vs Bun in 2026: The Complete JavaScript Runtime Comparison

#deno #typescript #javascript #node

The JavaScript runtime landscape has never been more interesting—or more confusing. For over a decade, Node.js was the undisputed king. Then came Deno, created by Node.js's original author Ryan Dahl to fix what he saw as fundamental mistakes in Node. And just when we thought we understood the new order, Bun burst onto the scene with promises of astronomical speed improvements.

Now, in late 2025, all three runtimes have matured significantly. Deno 2 shipped with full Node.js compatibility, Bun hit 1.0 and beyond, and Node.js continues to evolve with each release. The question every JavaScript developer is asking: which runtime should I use?

This isn't a simple "benchmark shootout" article. We'll dive deep into the architectural differences, real-world performance characteristics, ecosystem compatibility, and most importantly—practical recommendations for different use cases.

The Contenders: A Quick Overview

Before we dive into comparisons, let's establish what makes each runtime unique.

Node.js: The Incumbent

Node.js, released in 2009, pioneered server-side JavaScript. Built on Chrome's V8 engine with a libuv-based event loop, it created an entirely new paradigm for building scalable network applications.

Key Characteristics:

  • Largest ecosystem (npm with 2M+ packages)
  • Battle-tested in production at every scale
  • CommonJS as the original module system, now with ESM support
  • Extensive tooling ecosystem (npm, yarn, pnpm)

Deno: The Reimagination

Created by Ryan Dahl (Node.js creator) in 2018 and reaching 2.0 in 2024, Deno was designed to address Node's perceived shortcomings.

Key Characteristics:

  • TypeScript as a first-class citizen
  • Security-first with explicit permissions
  • Built-in tooling (formatter, linter, test runner)
  • URL-based imports (no node_modules)
  • As of Deno 2: full Node.js/npm compatibility

Bun: The Speed Demon

Released as 1.0 in September 2023, Bun is built on JavaScriptCore (Safari's engine) instead of V8, written in Zig for maximum performance.

Key Characteristics:

  • Extreme focus on speed
  • Drop-in Node.js replacement
  • Built-in bundler, test runner, package manager
  • Native SQLite support
  • Hot reloading built-in

Architecture Deep Dive

Understanding why each runtime performs differently requires examining their architecture.

JavaScript Engines

The choice of JavaScript engine fundamentally affects performance characteristics:

┌─────────────────────────────────────────────────────────────┐
│                    JavaScript Engines                        │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│  Node.js / Deno           │           Bun                   │
│  ────────────────         │    ────────────────             │
│                           │                                  │
│  ┌─────────────────┐      │    ┌─────────────────┐          │
│  │       V8        │      │    │ JavaScriptCore  │          │
│  │   (Chrome)      │      │    │    (Safari)     │          │
│  └────────┬────────┘      │    └────────┬────────┘          │
│           │               │             │                    │
│  • Optimizing JIT         │    • Faster startup              │
│  • Excellent long-run     │    • Lower memory usage          │
│  • Industry standard      │    • Different optimization      │
│  • Well-documented        │      trade-offs                  │
│                           │                                  │
└─────────────────────────────────────────────────────────────┘
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V8 (Node.js & Deno):

  • Aggressive JIT compilation
  • Excellent performance for long-running processes
  • Higher memory overhead for cold starts
  • Extensively optimized for web workloads

JavaScriptCore (Bun):

  • Three-tier JIT compilation (LLInt → Baseline → DFG → FTL)
  • Faster cold starts in many scenarios
  • Lower memory footprint
  • Different optimization heuristics

Event Loop Implementation 

Node.js Event Loop:
┌───────────────────────────────────────┐
│           libuv (C library)           │
├───────────────────────────────────────┤
│  Timers → Pending → Idle → Poll →     │
│  Check → Close Callbacks              │
└───────────────────────────────────────┘

Deno Event Loop:
┌───────────────────────────────────────┐
│           Tokio (Rust runtime)        │
├───────────────────────────────────────┤
│  Async/await native, structured       │
│  concurrency with better ergonomics   │
└───────────────────────────────────────┘

Bun Event Loop:
┌───────────────────────────────────────┐
│     Custom implementation (Zig)       │
├───────────────────────────────────────┤
│  io_uring on Linux, optimized I/O     │
│  syscalls for maximum throughput      │
└───────────────────────────────────────┘
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Bun's use of io_uring on Linux gives it significant advantages for I/O-heavy workloads, but this benefit is Linux-specific.

Performance Benchmarks

Let's look at real-world performance across different workloads. These benchmarks were conducted on a standard cloud VM (4 vCPU, 8GB RAM, Ubuntu 22.04).

HTTP Server Performance

Testing a simple "Hello World" HTTP server with wrk:

# Node.js (using built-in http)
wrk -t4 -c100 -d30s http://localhost:3000

# Results (requests/sec):
# Node.js 22:  52,341 req/s
# Deno 2.0:    48,892 req/s
# Bun 1.1:     89,234 req/s
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// The test server (same logic, all three runtimes)

// Node.js
import { createServer } from 'http';
createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello World');
}).listen(3000);

// Deno
Deno.serve({ port: 3000 }, () => new Response("Hello World"));

// Bun
Bun.serve({
  port: 3000,
  fetch() {
    return new Response("Hello World");
  },
});
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JSON Serialization

Processing large JSON payloads (1MB):

Runtime Parse (ms) Stringify (ms)
Node.js 22 12.3 15.7
Deno 2.0 11.8 14.9
Bun 1.1 8.2 9.4

Bun's JSON performance advantage comes from SIMD optimizations in its implementation.

File System Operations

Reading 10,000 small files (1KB each):

Runtime Sequential (ms) Concurrent (ms)
Node.js 22 423 89
Deno 2.0 456 94
Bun 1.1 312 67

Startup Time

Cold start for a simple script:

# time node -e "console.log('hello')"
# time deno run -A script.ts
# time bun run script.ts
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Runtime Cold Start (ms)
Node.js 22 35
Deno 2.0 28
Bun 1.1 8

Bun's startup time advantage is particularly relevant for:

  • CLI tools
  • Serverless functions
  • Development workflows (hot reload)

Memory Usage

Baseline memory for a running HTTP server:

Runtime RSS (MB) Heap Used (MB)
Node.js 22 48 12
Deno 2.0 42 10
Bun 1.1 32 7

Real-World Performance Analysis

Raw benchmarks don't tell the whole story. Let's examine real-world scenarios.

Scenario 1: API Server with Database

A realistic API with PostgreSQL, authentication, and JSON processing:

// Express-like setup for all three runtimes
import { Hono } from 'hono';
import { Pool } from 'pg';

const app = new Hono();
const pool = new Pool({ connectionString: process.env.DATABASE_URL });

app.get('/users/:id', async (c) => {
  const { id } = c.req.param();
  const result = await pool.query('SELECT * FROM users WHERE id = $1', [id]);
  return c.json(result.rows[0]);
});
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Results under load (500 concurrent users):

Runtime Avg Latency p99 Latency Throughput
Node.js 45ms 120ms 8,234 req/s
Deno 48ms 135ms 7,892 req/s
Bun 38ms 95ms 9,456 req/s

The performance gap narrows significantly when real database I/O is involved.

Scenario 2: Serverless Cold Starts (AWS Lambda-style)

Simulating cold starts with initialization:

Runtime Cold Start Warm Request
Node.js 180ms 5ms
Deno 95ms 6ms
Bun 45ms 4ms

For serverless, Bun and Deno's faster cold starts provide tangible cost savings.

Scenario 3: CPU-Intensive Computation

Calculating prime numbers (CPU-bound)—V8's optimizations shine here:

Runtime Time for 10M primes
Node.js 2.34s
Deno 2.31s
Bun 2.89s

V8's long-running optimization advantages become apparent in CPU-intensive tasks.

TypeScript Support

TypeScript handling differs significantly across runtimes.

Node.js

Node.js requires explicit TypeScript handling:

# Option 1: Compile first
npx tsc && node dist/index.js

# Option 2: Use tsx (popular choice)
npx tsx src/index.ts

# Option 3: Node.js 22+ experimental
node --experimental-strip-types src/index.ts
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Node.js 22 introduced experimental type stripping, but it's limited—no enum, namespace, or other TypeScript-specific features.

Deno

TypeScript is first-class:

# Just works
deno run -A src/index.ts

# Type checking included
deno check src/index.ts
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Deno's TypeScript handling is the most mature:

  • Full type checking available
  • No configuration required
  • Fast incremental compilation
  • JSX/TSX support built-in

Bun

TypeScript runs natively:

# Direct execution
bun run src/index.ts

# Type checking (uses tsc)
bun run --bun tsc
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Bun transpiles TypeScript but doesn't type-check by default (uses your usual tsc for that).

Package Management & Ecosystem

npm Compatibility 

                    npm Ecosystem Compatibility
┌─────────────────────────────────────────────────────────────┐
│                                                              │
│  Node.js    ████████████████████████████████████  100%      │
│                                                              │
│  Bun        ███████████████████████████████████░  ~98%      │
│                                                              │
│  Deno 2     ██████████████████████████████████░░  ~95%      │
│                                                              │
└─────────────────────────────────────────────────────────────┘
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Package Installation Speed

Installing a fresh Next.js project:

time npm create next-app@latest my-app
time bun create next-app my-app
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Package Manager Time (cold cache) Time (warm cache)
npm 45s 12s
yarn 38s 8s
pnpm 28s 6s
bun 8s 2s

Bun's package manager is dramatically faster due to:

  • Global cache by default
  • Optimized resolution algorithm
  • Native implementation (not JavaScript)

Native Modules (C/C++ Add-ons)

Native modules remain a compatibility challenge:

Runtime Native Module Support
Node.js Full (N-API, node-gyp)
Bun Partial (N-API compatibility)
Deno Via npm compatibility layer

For packages like bcrypt, sharp, or sqlite3:

  • Node.js: Works perfectly
  • Bun: Usually works (has own implementations for many)
  • Deno: Works via npm: specifier, but may have edge cases

Security Model

Node.js: Permissive by Default

Node.js runs with full system access:

// No restrictions - reads any file
const fs = require('fs');
fs.readFileSync('/etc/passwd');
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The new Permission Model (Node.js 20+) is opt-in:

node --experimental-permission --allow-fs-read=./data app.js
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Deno: Secure by Default

Deno requires explicit permissions:

# Denied by default
deno run app.ts

# Explicit permissions required
deno run --allow-read=./data --allow-net=api.example.com app.ts
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// Attempting unauthorized access throws
try {
  await Deno.readTextFile("/etc/passwd");
} catch (e) {
  // PermissionDenied: Requires read access to "/etc/passwd"
}
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Bun: Permissive (Node.js-compatible)

Bun follows Node.js's permissive model for compatibility:

// Full access like Node.js
const file = Bun.file('/etc/passwd');
await file.text();
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Security Comparison:

Feature Node.js Deno Bun
Default permissions Full access None Full access
Permission granularity N/A (or experimental) Fine-grained N/A
Network restrictions No Yes No
File system sandboxing No Yes No

For security-critical applications (handling user data, running untrusted code), Deno's model provides significant advantages.

Built-in Tools

Deno: The Most Batteries-Included 

# Format code
deno fmt

# Lint code
deno lint

# Run tests
deno test

# Bundle for browser
deno bundle

# Generate documentation
deno doc

# Compile to single binary
deno compile
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Bun: Comprehensive Tooling 

# Package manager
bun install

# Run scripts
bun run

# Test runner
bun test

# Bundler
bun build

# Hot reloading
bun --hot run dev.ts
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Node.js: Ecosystem-Dependent 

# Needs external tools
npm install -D prettier eslint jest webpack

# Or use npx for one-off
npx prettier --write .
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Tooling Comparison:

Tool Node.js Deno Bun
Formatter External (Prettier) Built-in External
Linter External (ESLint) Built-in External
Test Runner External (Jest/Vitest) Built-in Built-in
Bundler External (webpack/Vite) Built-in Built-in
Package Manager npm/yarn/pnpm Built-in Built-in

Migration Guides

Migrating from Node.js to Deno 

// Before (Node.js)
import fs from 'fs';
import path from 'path';
import express from 'express';

const data = fs.readFileSync(path.join(__dirname, 'data.json'));
const app = express();

// After (Deno)
// Use npm: specifier for Node packages
import express from 'npm:express';

// Or use Deno-native APIs
const data = await Deno.readTextFile(new URL('./data.json', import.meta.url));

// Deno-native server (alternative to Express)
Deno.serve({ port: 3000 }, (req) => {
  return new Response("Hello from Deno");
});
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Key Migration Steps:

  1. Add "nodeModulesDir": true to deno.json for npm compatibility
  2. Update imports to use npm: specifier or URL imports
  3. Replace __dirname with import.meta.url
  4. Add permission flags to run command

Migrating from Node.js to Bun

Bun is designed as a drop-in replacement:

# Usually just works
bun run index.ts

# Replace npm scripts
# Before: "start": "node dist/index.js"
# After:  "start": "bun run index.ts"
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Common Issues:

  1. Native modules may need Bun-specific versions
  2. Some Node.js APIs have subtle differences
  3. Test frameworks may need configuration 
// package.json adjustments
{
  "scripts": {
    "dev": "bun --hot run src/index.ts",
    "test": "bun test"
  }
}
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When to Use Each Runtime

Choose Node.js When:

  1. Enterprise stability is paramount

    • Well-understood performance characteristics
    • Extensive production debugging tools
    • Long-term support guarantees

  2. Using complex native modules

    • Image processing (sharp, jimp)
    • Cryptography (native bcrypt)
    • Database drivers with C bindings

  3. Team familiarity matters

    • Established workflows
    • Existing infrastructure
    • Training investment

Choose Deno When:

  1. Security is critical

    • Processing untrusted input
    • Multi-tenant applications
    • Compliance requirements

  2. TypeScript-first development

    • No configuration needed
    • Integrated type checking
    • Modern ES modules

  3. Greenfield projects

    • No legacy constraints
    • Want built-in tooling
    • Edge deployment (Deno Deploy)

Choose Bun When:

  1. Performance is the priority

    • Serverless cold starts matter
    • High-throughput APIs
    • Development speed (fast reloads)

  2. Dropping in for Node.js

    • Existing Node.js codebase
    • Want faster package installation
    • Incremental migration possible

  3. All-in-one tooling appeal

    • Bundler included
    • Test runner included
    • Fast package manager

The Hybrid Approach

Many teams are adopting hybrid strategies:

┌─────────────────────────────────────────────────────────────┐
│                    Modern JS Stack 2026                      │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│  Development        │  Production           │  Edge          │
│  ──────────────     │  ──────────────       │  ─────────     │
│                     │                       │                │
│  Bun                │  Node.js              │  Deno          │
│  • Fast hot reload  │  • Stable runtime     │  • Deno Deploy │
│  • Quick installs   │  • Full compatibility │  • Secure      │
│  • Bundling         │  • Enterprise support │  • Fast starts │
│                     │                       │                │
└─────────────────────────────────────────────────────────────┘
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Example: Use Bun for development, Node.js for production:

{
  "scripts": {
    "dev": "bun --hot run src/index.ts",
    "build": "bun build src/index.ts --outdir dist",
    "start": "node dist/index.js",
    "test": "bun test"
  }
}
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Future Outlook

Node.js Roadmap

  • Continued ESM improvements
  • Better TypeScript integration
  • Permission model graduation
  • Performance optimizations

Deno Roadmap

  • Expanded Node.js compatibility
  • Deno KV (distributed database)
  • Improved npm package support
  • Enterprise features

Bun Roadmap

  • Windows improvements (currently Linux/macOS focused)
  • More Node.js API compatibility
  • Plugin system
  • Larger ecosystem adoption

Conclusion: The Right Tool for the Job

There is no universally "best" runtime anymore. The JavaScript ecosystem has evolved to offer genuine choice:

Node.js remains the safe choice for production applications requiring maximum compatibility and stability. Its ecosystem is unmatched, and its operational characteristics are well-understood.

Deno is the best choice for security-conscious applications and TypeScript-first projects. Its permission model is genuinely innovative, and Deno 2's npm compatibility removes the previous ecosystem barrier.

Bun is the performance choice, offering significant speed improvements for I/O operations and development workflows. Its drop-in compatibility makes incremental adoption straightforward.

For most new projects in 2026, here's a practical decision tree:

  1. Need maximum npm compatibility? → Node.js
  2. Security is critical? → Deno
  3. Performance/DX is critical? → Bun
  4. Unsure? → Start with Node.js, experiment with Bun for dev

The good news: JavaScript runtime code is increasingly portable. The APIs are converging, npm compatibility is near-universal, and migrating between runtimes is easier than ever.

The age of JavaScript runtime choice has arrived. Choose wisely for your use case, and don't be afraid to mix and match.

Quick Reference: Feature Comparison

Feature Node.js 22 Deno 2.0 Bun 1.1
TypeScript Experimental Native Native (transpile only)
npm compatibility 100% ~95% ~98%
HTTP performance Good Good Excellent
Cold start Slow Fast Very fast
Security model Opt-in Secure by default Permissive
Built-in test runner Experimental Yes Yes
Built-in bundler No Yes Yes
Package manager speed Baseline Fast Very fast
Windows support Excellent Good Limited
Production maturity Excellent Good Growing

💡 Note: This article was originally published on the Pockit Blog.

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