Deno and Bun: The New JavaScript Runtimes You Need to Know in 2025

The JavaScript Runtime Landscape Is Shifting

For over a decade, Node.js reigned as the undisputed king of server-side JavaScript. It powered everything from tiny microservices to massive enterprise platforms, and its npm ecosystem grew into the largest package registry on Earth — surpassing 2.5 million packages in 2025.

But dominance breeds complacency, and complacency invites competition.

Enter Deno and Bun — two ambitious JavaScript runtimes that have matured rapidly over the past two years. Both aim to fix what Node.js got wrong while pushing the boundaries of performance, developer experience, and security. If you build anything with JavaScript or TypeScript in 2025, these two names deserve your full attention.

At Lueur Externe, where we’ve been building high-performance web solutions since 2003, we’ve been closely tracking and testing these runtimes across client projects. Here’s everything you need to know to make an informed decision.

Deno 2: The Mature Challenger

A Brief History

Deno was created by Ryan Dahl — the same person who created Node.js. In his now-famous 2018 JSConf talk, “10 Things I Regret About Node.js,” Dahl outlined fundamental design mistakes in Node and introduced Deno as his attempt to start over.

The first stable release (Deno 1.0) arrived in May 2020. It was opinionated, principled, and… not very practical for most teams. Lack of npm compatibility meant rewriting dependencies or going without.

That all changed with Deno 2, released in October 2024. This release was a watershed moment.

Key Features of Deno 2

• Full Node.js and npm compatibility — You can now import npm packages directly. Most Express, Fastify, and other Node.js frameworks run on Deno without modification.
• Native TypeScript support — No tsconfig.json, no ts-node, no build step. Write .ts files and run them.
• Built-in security model — By default, Deno denies access to the file system, network, and environment variables. You explicitly grant permissions with flags like --allow-net and --allow-read.
• Standard library — A curated, audited standard library (@std) that covers formatting, testing, HTTP servers, path manipulation, and more.
• Web-standard APIs — Deno uses fetch(), Request, Response, WebSocket, and other browser APIs natively. Code you write for Deno often runs in the browser with minimal changes.
• Built-in tooling — Formatter (deno fmt), linter (deno lint), test runner (deno test), and bundler — all included.
• Deno Deploy — A global edge runtime for deploying Deno applications across 35+ regions with zero configuration.

Deno in Practice

Here’s a simple HTTP server in Deno 2:

// server.ts — run with: deno run --allow-net server.ts
Deno.serve({ port: 3000 }, (req: Request): Response => {
  const url = new URL(req.url);
  if (url.pathname === "/api/hello") {
    return Response.json({ message: "Hello from Deno 2!" });
  }
  return new Response("Not Found", { status: 404 });
});

console.log("Server running on http://localhost:3000");

Notice how it uses the standard Request and Response objects — the same ones you’d use in a Service Worker or Cloudflare Worker. No third-party framework required for basic routing.

Who Should Use Deno?

• Teams that prioritize security and want permission-based execution
• Projects using TypeScript heavily (no config overhead)
• Developers deploying to edge platforms (Deno Deploy, Supabase Edge Functions)
• Anyone who wants a batteries-included developer experience

Bun: The Speed Demon

A Brief History

Bun was created by Jarred Sumner and first released as a beta in July 2022. Its stable 1.0 release came in September 2023, and by early 2025, Bun has reached version 1.2+ with significant improvements across the board.

Unlike Deno, which was born from philosophical concerns about Node’s design, Bun was born from a single obsession: raw performance.

Key Features of Bun

• JavaScriptCore engine — Instead of V8 (used by Node and Deno), Bun uses Apple’s JavaScriptCore (from WebKit). This gives it a startup-time advantage of up to 4x over Node.js.
• Written in Zig — Bun’s core is implemented in Zig, a low-level systems language that enables fine-grained memory control and extreme optimization.
• All-in-one toolkit — Bun is a runtime, package manager, bundler, test runner, and transpiler. One binary replaces node, npm, npx, webpack, esbuild, and jest.
• Near-complete Node.js compatibility — Most node_modules work out of the box. Express, Next.js, Nuxt, Hono, and thousands of other packages run on Bun.
• Blazing-fast package manager — bun install is consistently 20-30x faster than npm install thanks to global caching and hardlinked node_modules.
• Native SQLite support — bun:sqlite provides a built-in, high-performance SQLite driver.
• Hot reloading — bun --watch provides instant file-watching and restart, faster than nodemon.

Bun in Practice

Here’s the equivalent HTTP server in Bun:

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

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

The API is strikingly similar to Deno’s — both embrace web standards. But behind the scenes, Bun’s implementation is optimized for throughput at every level.

Who Should Use Bun?

• Teams where performance is the top priority (APIs, real-time applications)
• Projects that need fast CI/CD pipelines (Bun’s install and build speed cuts minutes off workflows)
• Developers who want a single tool to replace multiple dependencies
• Anyone tired of slow npm install and complex build configurations

Deno vs. Bun vs. Node.js: The 2025 Comparison

Let’s put all three runtimes side by side:

Feature	Node.js 22	Deno 2	Bun 1.2
Engine	V8	V8	JavaScriptCore
Language	C++	Rust	Zig
TypeScript Support	Via transpiler	Native	Native
Package Manager	npm / yarn / pnpm	deno add + npm compat	bun install
Security Model	None (full access)	Permission-based	None (full access)
Built-in Test Runner	node --test (basic)	deno test (mature)	bun test (Jest-compatible)
Built-in Bundler	No	Yes	Yes
Startup Time	~40ms	~30ms	~10ms
HTTP Throughput (req/s)	~55,000	~70,000	~110,000
npm Compatibility	Full	~95%	~97%
Ecosystem Maturity	★★★★★	★★★★☆	★★★☆☆
Production Adoption	Massive	Growing fast	Early but accelerating

Benchmarks are approximate and vary by workload, hardware, and configuration. Numbers above reflect common HTTP-serving benchmarks on equivalent hardware (2024–2025 community tests).

Performance Deep Dive

When it comes to raw numbers, Bun consistently leads:

• HTTP serving: Bun handles roughly 2x the requests per second compared to Node.js and about 1.5x more than Deno in synthetic benchmarks.
• Startup time: Bun boots in approximately 10 milliseconds, compared to ~30ms for Deno and ~40ms for Node. This matters enormously for serverless and edge functions where cold starts impact user experience.
• Package installation: bun install on a large project (1,000+ dependencies) typically completes in 2-5 seconds, where npm install may take 60-90 seconds.

However, benchmarks don’t tell the whole story. In real-world applications with complex business logic, database queries, and external API calls, the runtime overhead becomes a smaller percentage of total response time. The practical difference between 55,000 and 110,000 requests per second rarely matters when your database query takes 50ms.

Security: Deno’s Unique Advantage

One area where Deno stands alone is security by default. Consider this scenario: you install an npm package that has a malicious postinstall script. In Node.js and Bun, that script runs with full access to your file system, network, and environment variables. In Deno, it would be blocked unless you explicitly grant permissions.

This is not theoretical. Supply chain attacks via npm packages have increased 150% between 2022 and 2024 according to Snyk’s State of Open Source Security report. Deno’s permission model is a meaningful defense layer.

# Deno: explicitly grant only the permissions your app needs
deno run --allow-net=api.example.com --allow-read=./data server.ts

# The script CANNOT access other network hosts or file paths

For security-sensitive applications — financial services, healthcare, government — this model is compelling.

Real-World Adoption in 2025

Both runtimes have moved well beyond the “toy project” stage:

Deno adoption highlights:

• Supabase Edge Functions run entirely on Deno
• Netlify Edge Functions are powered by Deno
• Slack’s next-generation platform uses Deno
• Deno Deploy serves billions of requests monthly across its edge network

Bun adoption highlights:

• Several Y Combinator startups have built their backends entirely on Bun
• Oven (the company behind Bun) raised $7 million in funding
• Major open-source projects like Elysia.js are Bun-native
• Companies report 40-60% reductions in CI/CD pipeline times after switching to Bun for builds and installs

Practical Advice: Which Should You Choose?

After extensive testing across dozens of client projects, here is the framework we recommend at Lueur Externe:

Choose Deno if:

• Security is a primary concern
• You’re building for edge/serverless deployment
• Your team writes TypeScript exclusively
• You value standards compliance and long-term API stability
• You want a polished, opinionated developer experience

Choose Bun if:

• Raw performance and throughput are critical
• You need the fastest possible CI/CD pipelines
• You want a drop-in Node.js replacement with minimal migration effort
• You’re building real-time applications (WebSocket servers, gaming backends)
• You want one tool to handle runtime, bundling, testing, and package management

Stick with Node.js if:

• You have a large existing codebase with deep Node-specific dependencies
• Your team relies on specific native add-ons (e.g., node-gyp-based modules)
• You need the widest possible ecosystem support and community resources
• Enterprise compliance requires battle-tested, LTS-supported runtimes

Migration Tips

If you’re considering moving an existing Node.js project to Deno or Bun, here are some practical tips:

1. Start with your test suite. Both deno test and bun test can run most Jest-compatible tests. If your tests pass, your application likely works.
2. Check native add-ons. Modules that use node-gyp or native C++ bindings are the most common breaking point. Look for pure-JS alternatives.
3. Run both runtimes in CI. Before fully committing, add a parallel CI step that runs your app on the new runtime. Catch issues early.
4. Benchmark your actual workload. Don’t rely on synthetic benchmarks. Test with your real database, your real APIs, and your real traffic patterns.
5. Migrate gradually. Start with internal tools, development scripts, or non-critical microservices before touching your main production application.

The Bigger Picture: Why This Matters

The emergence of Deno and Bun signals something deeper than just “new tools.” It represents a philosophical shift in how we think about JavaScript infrastructure:

• TypeScript is no longer optional. Both new runtimes treat TypeScript as a first-class citizen. The era of separate compilation steps is ending.
• Web standards are winning. fetch(), Request, Response, URL, WebSocket — the browser APIs are becoming the universal JavaScript API.
• All-in-one tooling is the future. The days of installing five separate tools (runtime, package manager, bundler, linter, test runner) are numbered.
• Performance expectations are rising. Users and businesses expect faster cold starts, higher throughput, and lower latency. Runtimes that can’t deliver will fall behind.

For agencies and development teams building modern web applications, understanding these runtimes is no longer optional — it’s a competitive advantage.

Conclusion: The Runtime You Choose Matters More Than Ever

In 2025, the JavaScript runtime you choose shapes your application’s performance, security posture, developer productivity, and deployment strategy. Node.js remains a solid, well-supported choice for many projects. But Deno and Bun have matured into genuinely compelling alternatives that solve real problems Node.js was never designed to address.

Deno offers the best security model and the cleanest developer experience. Bun offers unmatched speed and an all-in-one approach that simplifies toolchains. Both support TypeScript natively, embrace web standards, and are production-ready.

The best approach? Evaluate both against your specific requirements, run benchmarks on your actual workload, and choose deliberately.

At Lueur Externe, our development team has been building, benchmarking, and deploying applications on all three runtimes since early 2024. Whether you’re starting a new project, optimizing an existing platform, or planning a migration strategy, our experts can help you make the right choice — and execute it flawlessly. Get in touch with us to discuss your next project.