Deno 1 vs Deno 2: Key Differences and When to Use Each

The Deno 2 release introduces improved performance, enhanced security defaults, and updated APIs compared to Deno 1. It also features better module resolution and native support for new web standards, making it more efficient and secure for modern JavaScript and TypeScript development.

Quick Comparison

Here is a quick side-by-side comparison of key aspects between Deno 1 and Deno 2.

Aspect	Deno 1	Deno 2
Release Date	May 2020	Expected 2024
Performance	Good, initial stable release	Improved runtime speed and startup time
Security	Permission-based, manual flags	Stricter defaults and finer-grained controls
Module Resolution	Basic URL and local file support	Enhanced caching and import maps support
API Changes	Stable but evolving	Refined APIs with better web standards alignment
Native Web APIs	Partial support	Expanded native support for web APIs

Key Differences

Deno 2 builds on the foundation of Deno 1 by focusing on performance improvements such as faster startup times and reduced memory usage. This makes running scripts and servers more efficient, especially for larger projects.

Security in Deno 2 is enhanced with stricter permission defaults and more granular control over file system, network, and environment access. This reduces accidental security risks and aligns better with modern security practices.

API changes in Deno 2 include updates to module resolution, supporting import maps more robustly and improving caching mechanisms. Additionally, Deno 2 expands native support for web APIs like WebSocket and Fetch, making it easier to write cross-platform code that works both in browsers and on the server.

Code Comparison

Here is a simple example showing how to fetch data from an API in Deno 1.

typescript

const response = await fetch('https://api.github.com');
const data = await response.json();
console.log(data.current_user_url);

Output

https://api.github.com/user

Deno 2 Equivalent

The same fetch example in Deno 2 benefits from improved performance and stricter security permissions.

typescript

const response = await fetch('https://api.github.com');
const data = await response.json();
console.log(data.current_user_url);

Output

https://api.github.com/user

When to Use Which

Choose Deno 2 when you want the latest performance improvements, enhanced security, and better support for modern web APIs. It is ideal for new projects that need efficient runtime and stricter security out of the box.

Use Deno 1 if you rely on legacy code or third-party modules not yet updated for Deno 2. It remains stable and supported but lacks the latest enhancements.

Key Takeaways

Deno 2 offers faster performance and stricter security than Deno 1.

API and module resolution improvements in Deno 2 support modern web standards better.

Use Deno 2 for new projects to benefit from the latest features and security.

Deno 1 is suitable for legacy compatibility and existing stable codebases.

Both versions share similar coding patterns but differ in runtime behavior and defaults.