Bun vs Deno: Which Is Better for JavaScript Runtimes in 2026?

Bun starts in ~5-10ms, the fastest of any JavaScript runtime. Written in Zig with JavaScriptCore, it's optimized for instant cold starts. CLI tools and serverless functions benefit enormously.

Deno starts in ~20-40ms — faster than Node.js but 3-5x slower than Bun. V8 initialization overhead is the bottleneck. Fine for servers, but noticeable for short-lived scripts.

Bun.serve() consistently benchmarks at 150-250K req/sec in synthetic tests. The built-in HTTP server is implemented in native code, bypassing JavaScript overhead for the hot path.

Deno.serve() handles 100-180K req/sec with the Hyper-based Rust HTTP stack. Competitive with Bun for real-world workloads where business logic dominates. Flash server was replaced with a more stable implementation.

bun install is the fastest package manager in the JavaScript ecosystem. Global binary cache with hardlinks means repeat installs take under a second. Fresh Next.js install in 2-3 seconds.

Deno 2 supports npm packages via npm: specifiers and node_modules. Installation speed is similar to npm — not a focus area for Deno. URL imports skip installation entirely but trade caching predictability.

Bun's native Zig-based I/O layer is extremely fast. Bun.file() reads are 3-5x faster than Node.js fs operations. SQLite is built in and benchmarks faster than better-sqlite3 on Node.

Deno uses Rust's tokio for async I/O, which is fast but adds serialization overhead between Rust and V8. File operations are comparable to Node.js. Deno KV provides built-in key-value storage.

Native TypeScript execution with zero config — just bun run file.ts. Supports all TypeScript syntax including decorators and const enums. Uses its own transpiler, not tsc, so type-checking requires a separate step.

First-class TypeScript from day one with built-in type checking via tsc integration. Deno's LSP provides real-time type errors in your editor. The TypeScript experience is the most polished of any runtime.

Bun includes a package manager, bundler, test runner, and script runner out of the box. bun:test is Jest-compatible and 5-10x faster. Bun.build handles most bundling needs. One binary does everything.

Deno includes a formatter (deno fmt), linter (deno lint), test runner (deno test), benchmarker (deno bench), and documentation generator. More opinionated than Bun — the tools enforce consistent style.

Bun implements many Web APIs (fetch, Response, Request, WebSocket, crypto.subtle) but prioritizes Node.js compatibility over web standards when they conflict. Some Web APIs have subtle behavior differences.

Deno is the most web-standards-compliant runtime. Code written for Deno often runs in browsers unchanged. fetch, streams, Web Crypto, and URL all match the browser specification exactly.

Bun's documentation has improved but remains thinner than Deno's. API references cover the basics. Community content is growing but Stack Overflow answers are still sparse for edge cases.

Deno has excellent documentation with interactive examples, a manual, and thorough API references. Ryan Dahl's talks and Deno's blog provide strong conceptual grounding. The community is smaller but engaged.

~95%+ npm compatibility. Most packages work without changes. Native modules (node-gyp) are the main gap. Bun's goal is to be a drop-in Node.js replacement, and it's close.

Deno 2 added npm: specifiers and package.json support, making most npm packages usable. Compatibility is good but slightly behind Bun for packages that rely on Node.js-specific internals.

Next.js, Nuxt, SvelteKit, Astro, Hono, Elysia, and Express all work on Bun. The Elysia framework is Bun-native and extremely fast. Most JavaScript frameworks target Bun as a first-class runtime.

Fresh is Deno's native web framework (Preact-based, islands architecture). Next.js and Astro work via npm compatibility. Hono has first-class Deno support. The framework ecosystem is smaller but growing.

Supported on Railway, Fly.io, Render, and Docker. AWS Lambda support exists but isn't as mature as Node.js. Some platforms haven't officially added Bun support yet.

Deno Deploy is a purpose-built edge hosting platform with zero-config deployments and globally distributed. Also works on Fly.io, Railway, Docker. Deno Deploy's simplicity is a genuine advantage.

Bun has no standard library — it relies on npm packages for utilities. Built-in APIs cover runtime needs (HTTP, file I/O, SQLite) but there's no curated utility collection like Go's stdlib.

Deno's standard library (jsr:@std) is curated, reviewed, and versioned. Includes modules for path, fs, http, testing, encoding, crypto, and more. Quality is consistently high, like Go or Python's stdlib.

No permission system — Bun runs with full system access like Node.js. Any npm package can read files, make network requests, or execute commands. You trust your dependencies or use OS-level sandboxing.

Deno's permission system is unique among runtimes. Scripts must explicitly request --allow-net, --allow-read, --allow-write, etc. A compromised npm dependency can't silently exfiltrate data. This is a real security advantage.

Bun is production-ready for most workloads but still younger than Node.js or Deno. Edge cases surface under heavy load. Memory leak reports are less frequent than 2024 but still occur in complex applications.

Deno 2 is stable and production-tested by Netlify Edge Functions, Slack, and Deno Deploy's own infrastructure. V8's garbage collector is well-understood. Fewer surprises in long-running processes than Bun.

WebKit Inspector via --inspect. Less mature than Chrome DevTools. APM tooling (Datadog, Sentry) has basic Bun support but not all features work. Profiling is more limited than V8-based runtimes.

Chrome DevTools integration via --inspect (V8-based). Familiar profiling, heap snapshots, and flame charts. OpenTelemetry support is built in. APM tools work well since Deno shares V8 with Node.js.

Bun moves fast and occasionally introduces breaking changes between minor versions. The API surface is still stabilizing. Lockfile format has changed. Pinning versions is important.

Deno follows semantic versioning strictly since 2.0. Breaking changes only happen in major versions. The commitment to web standards means APIs rarely change — if it works in the browser, it works in Deno.