Bun vs. Deno 2.0: A Comprehensive Comparison for Modern JavaScript Development

As the landscape of JavaScript runtimes expands, Bun and Deno have emerged as two promising alternatives to Node.js, each offering unique features and optimizations. Bun is known for its speed and efficiency, while Deno emphasizes security, TypeScript support, and compatibility with modern standards. This comparison dives into the details of each runtime, helping developers choose the best option based on performance, compatibility, security, and ecosystem support.

Overview of Bun

Bun is a modern JavaScript runtime developed with a focus on speed and an all-in-one developer experience. It incorporates a fast bundler, transpiler, package manager, and task runner, all built on JavaScriptCore (the JavaScript engine used by Safari). Bun's goal is to streamline the JavaScript/TypeScript development process and deliver fast, efficient performance.

Key Features

• High Performance: Bun’s emphasis on speed comes from its use of JavaScriptCore, optimized for fast startup and execution.
• Integrated Tooling: Bun includes a built-in bundler, transpiler, package manager, and task runner, reducing the need for additional dependencies.
• TypeScript Support: TypeScript support is built-in, allowing developers to use TypeScript without additional setup.
• NPM Compatibility: Bun aims to be a drop-in replacement for Node.js, allowing most npm packages to work out-of-the-box.

Overview of Deno 2.0

Deno, developed by the creator of Node.js, is designed to address security and developer experience shortcomings in Node. Released in 2024, Deno 2.0 strengthens compatibility with Node.js, integrates npm support, and focuses on secure-by-default principles. Its native TypeScript support and comprehensive built-in tools make it ideal for modern JavaScript and TypeScript applications.

Key Features

• Security by Default: Deno enforces security at runtime by requiring explicit permissions for file, network, and environment access.
• Node.js Compatibility: Deno 2.0 has improved support for Node.js, allowing seamless use of npm packages and node_modules.
• TypeScript as a First-Class Citizen: TypeScript is natively supported, without needing extra configuration or compilers.
• Standard Library and Tooling: Deno includes a robust standard library, test runner, formatter, and linter, enabling a complete development environment.

Performance Comparison

Startup Speed

• Bun: With its JavaScriptCore engine, Bun is optimized for lightning-fast startup times, ideal for serverless applications where cold start times matter. This high-performance startup helps Bun execute tasks quickly and efficiently.
• Deno: While Deno is also designed to be efficient, its use of the V8 engine results in slightly slower startup times compared to Bun. This is especially noticeable in applications that require instant response, such as microservices and serverless functions.

Request Handling

• Bun: Known for its speed, Bun handles HTTP requests at over 50,000 requests per second, making it an excellent choice for high-throughput applications.
• Deno: Deno can handle around 20,000 requests per second, offering competitive performance but generally slower than Bun in raw throughput. However, for most applications, this difference may be marginal in real-world scenarios.

Performance Trade-offs

• Bun: The focus on speed makes Bun highly suitable for performance-critical applications, though it might lack some of the comprehensive security and tooling features of Deno.
• Deno: While slightly slower in benchmarks, Deno’s performance is balanced by its strong compatibility, security, and built-in tooling, which might better serve complex applications where security and standards compliance are paramount.

Server and Environment Compatibility

Server-Side Rendering and Server Compatibility

• Bun: Built with an emphasis on compatibility with existing JavaScript frameworks, Bun is suitable for server-side rendering (SSR) applications. Its performance advantage makes it highly effective for SSR, especially for applications built with React, Vue, or other popular frameworks.
• Deno: Deno supports server-side rendering through compatibility with frameworks like Fresh and Aleph.js, designed to work seamlessly with it. Deno’s security model and native TypeScript support can enhance SSR applications that prioritize code safety and maintainability.

Edge and Serverless Computing

• Bun: Bun’s fast startup times and high performance make it an ideal candidate for edge and serverless computing, where performance and low latency are essential. Bun’s compatibility with Vercel and other serverless platforms further extends its suitability for edge environments.
• Deno: Deno also works well in edge environments, particularly due to its strict permission model and comprehensive tooling. Platforms like Deno Deploy specifically cater to deploying Deno applications at the edge, and the LTS support in Deno 2.0 ensures production-grade stability.

Compatibility with Node.js and NPM

• Bun: Bun aims to be a drop-in replacement for Node.js, making most npm packages compatible without modification. It supports node_modules, CommonJS, and ES modules, which facilitates easier migration from Node.
• Deno: Deno 2.0 has made significant strides in Node.js compatibility. With its support for node_modules and npm, developers can run many Node applications directly in Deno without extensive refactoring. However, Deno’s module system is based on ES modules, so some CommonJS modules might need adaptation.

Security Model

• Bun: Bun doesn’t enforce a strict permissions model like Deno, though it offers a trustedDependencies setting in package.json for limited security control. While this approach allows more flexibility, it may not be suitable for security-sensitive applications.
• Deno: Security is a core part of Deno’s design. Deno enforces a “secure by default” philosophy, requiring permissions to access network, filesystem, and other sensitive operations. This approach makes it more secure out-of-the-box, especially valuable for applications handling sensitive data or operating in regulated environments.

Developer Experience

Both Bun and Deno prioritize developer experience, offering built-in tools to streamline development workflows.

Tooling and Built-in Utilities

• Bun: By bundling a package manager, bundler, and transpiler, Bun eliminates the need for several additional dependencies commonly used in Node.js projects. This all-in-one approach simplifies project setup, though some tools (e.g., linting, testing) might still require third-party solutions.

  bun create my-app
  bun run dev

• Deno: Deno includes a full suite of development tools: a linter, formatter, test runner, and dependency inspector. These built-in utilities make Deno highly productive, especially for TypeScript-based projects where code quality and type safety are essential.

  deno run --allow-net app.ts

TypeScript Support

• Bun: TypeScript is supported natively in Bun, making it easy to use TypeScript without additional configuration.
• Deno: Deno has first-class TypeScript support, as it was designed with TypeScript in mind. No separate build process is needed, and Deno interprets TypeScript files directly, which is highly advantageous for TypeScript-heavy codebases.

Ecosystem and Community Support

• Bun: As a relatively new runtime, Bun’s community is still growing. However, its compatibility with npm gives it access to a vast library ecosystem. Community support is expanding rapidly, with more projects being developed specifically for Bun.
• Deno: Deno has an established and active community focused on modern JavaScript and TypeScript practices. With Deno Deploy and an official standard library, Deno has a strong ecosystem tailored to secure, performant applications.

Pros and Cons Summary

Conclusion

Choosing between Bun and Deno 2.0 depends on your project’s priorities:

• Choose Bun if: Your project needs top-tier performance, rapid development, and integration with Node.js tools, and you prefer an all-in-one tool for bundling, transpiling, and managing packages.

• Choose Deno 2.0 if: Security, TypeScript integration, and developer tooling are critical for your project, especially for applications that require fine-grained access control or compatibility with existing Node.js modules.

Both Bun and Deno provide compelling features that cater to different needs in the JavaScript ecosystem, allowing developers to choose a runtime that best

aligns with their project goals.