Node.js has dominated JavaScript server-side development for over a decade, but two new challengers have emerged: Bun and Deno. Both offer modern approaches to JavaScript runtimes with built-in TypeScript support, security features, and improved developer experience. This guide compares both runtimes to help you choose the right one for your projects.
TL;DR - Quick Summary
Bun prioritizes speed and drop-in Node.js compatibility, featuring a JavaScriptCore engine and built-in bundler/test runner. Deno focuses on security, standards compliance, and first-class TypeScript support with granular permissions. Choose Bun for performance and ease of migration; choose Deno for security-first applications and modern web standards.
Key Takeaways
- Bun is significantly faster in most benchmarks, especially for I/O operations
- Deno has a more robust security model with explicit permissions
- Both have native TypeScript support without additional configuration
- Bun has better Node.js npm compatibility
- Deno has a more mature standard library and web API support
- Bun includes more built-in tools (bundler, test runner, package manager)
Runtime Overview
What is Bun?
Bun is an all-in-one JavaScript runtime built from scratch using Zig and JavaScriptCore. Released in 2022 by Oven, it aims to be a faster, more complete replacement for Node.js. Bun includes a runtime, bundler, test runner, and package manager in a single binary.
What is Deno?
Deno is a secure runtime for JavaScript and TypeScript created by Ryan Dahl, the original creator of Node.js. First released in 2020, Deno was designed to address Node.js design regrets. It features a secure-by-default model, built-in TypeScript support, and a standard library of reviewed modules.
Architecture Comparison
| Feature | Bun | Deno |
|---|---|---|
| Engine | JavaScriptCore (WebKit) | V8 |
| Implementation Language | Zig | Rust |
| First Released | 2022 | 2020 |
| Package Management | Built-in (bun) | URL imports + npm: |
| TypeScript | Built-in (fast transpile) | Built-in (type checking) |
| Security Model | Open by default | Permissions required |
| Standard Library | Minimal | Extensive (deno.land/std) |
| Config File | bunfig.toml | deno.json |
Performance Comparison
Benchmarks comparing execution speed and resource usage:
| Benchmark | Bun | Deno | Winner |
|---|---|---|---|
| HTTP requests/sec | ~190K | ~100K | Bun |
| JSON parsing | ~600K ops/s | ~450K ops/s | Bun |
| File I/O | ~60ms (100MB) | ~110ms (100MB) | Bun |
| Startup time | ~8ms | ~40ms | Bun |
| Memory usage | ~35MB | ~45MB | Bun |
Security Model
How each runtime handles security:
Open permissions by default. Code can access filesystem, network, and environment variables without restriction. This design prioritizes compatibility and ease of use, similar to Node.js behavior.
Security-first design. Code cannot access filesystem, network, or environment without explicit permissions by default. Use --allow-read, --allow-net flags to grant permissions.
# Deno - Explicit permissions required
deno run --allow-read --allow-net --allow-env app.ts
# Deno - Granular permissions
deno run --allow-read=/data --allow-net=api.example.com app.ts
# Bun - No permissions needed (runs with full access)
bun run app.ts
# Bun - Can be run with restricted permissions via container/sandboxBuilt-in Tooling
What tools come built-in with each runtime:
| Tool | Bun | Deno |
|---|---|---|
| Package Manager | bun install (built-in) | deno cache (URL-based) |
| Test Runner | bun:test (Jest-like) | Deno.test (built-in) |
| Bundler | bun build (built-in) | deno bundle (built-in) |
| Formatter | N/A (use Prettier) | deno fmt (built-in) |
| Linter | N/A (use ESLint) | deno lint (built-in) |
| Task Runner | bun run (package.json) | deno task (deno.json) |
| REPL | bun repl | deno repl |
| Doc Generator | N/A | deno doc (built-in) |
When to Use Each Runtime
Bun is Best For:
- Migrating from Node.js
- Performance-critical applications
- Need npm package compatibility
- All-in-one toolchain
- Fast startup times
- Large file I/O
Deno is Best For:
- Security-sensitive applications
- Modern web standards first
- Need built-in tools (fmt, lint)
- URL-based imports
- Audited standard library
- Edge deployments
Conclusion
Both Bun and Deno represent exciting advancements in JavaScript runtime technology. Bun excels when you need maximum performance and easy migration from Node.js, with its all-in-one tooling approach reducing complexity. Deno shines in security-conscious environments and when working with modern web standards, its explicit permission model providing defense in depth. In 2025, both are production-ready options, with the choice depending on your specific requirements around performance, security, and ecosystem compatibility.
FAQ
Can Bun and Deno run Node.js code?
Bun aims for drop-in Node.js compatibility and runs most Node.js code without changes. Deno requires some modifications to Node.js code, though compatibility has improved significantly with Deno 2.0. Both can use npm packages to varying degrees.
Is Deno more secure than Node.js and Bun?
Deno's security model is more explicit, requiring permissions for file system access, network, and environment variables. Bun and Node.js run with full permissions by default. However, all three can be secure when properly configured and deployed.
Which runtime is better for TypeScript?
Both have excellent TypeScript support without configuration. Deno's type checking is more strict by default. Bun focuses on fast transpilation without type checking, leaving that to your IDE or tsc. The choice depends on your preference for strictness vs speed.
Can I use npm packages with Deno?
Yes, Deno 2.0 significantly improved npm compatibility. You can import npm packages using npm: specifiers or import maps. However, not all npm packages work perfectly, especially those with native addons or Node.js-specific internals.
Is Bun production-ready?
Bun reached version 1.0 in 2023 and is being used in production by several companies. While newer than Deno, it has proven stable for many use cases. For critical applications, evaluate both based on your specific requirements.
Which has better web standards support?
Deno generally has better web standards support, implementing APIs like fetch, WebSocket, and others earlier and more completely. Bun also supports these APIs but focuses more on Node.js compatibility.
Can I migrate my Node.js app to these runtimes?
Migrating to Bun is generally easier due to its Node.js compatibility goals. Migrating to Deno may require more changes, particularly around module imports and file system operations. Start with non-critical services when migrating.
Do these runtimes work with Docker?
Yes, both have official Docker images. Bun's image is significantly smaller than Node.js, which can reduce deployment sizes. Deno also offers slim Docker images. Both work well in containerized environments.