Deno 2.0 Release Overview

• Largest update since 1.0, includes major changes like node's process global
• Final 1.x version was 1.46, now releasing 2.0 release candidate
• Philosophical shifts: preferring deno install over deprecated deno cache
• Created by Ryan Dahl (node.js creator) as response to regrets about node design
• Originally meant to reorganize node (D-no = undo node)

Global Variables Changes

• Window Global Removal
  • Window global caused compatibility issues with libraries
  • Libraries check for window to determine browser vs server environment
  • Led to bugs in libraries that would otherwise work in Deno
  • Deno 1.40 discouraged window globals, suggested Global this or self instead
• Process Global Addition
  • Widely requested feature for node compatibility
  • Previously required importing from node:process
  • Popular frameworks rely on process being in global scope
  • New no-process-global lint rule encourages explicit imports
  • Helps frameworks like Next.js work seamlessly

Dependency Management Improvements

• Deno Add Command Enhancements
  • Now handles specifiers with sub-paths
  • Automatically adds newest version when version not specified
  • Supports package format scope names starting with @
  • JSR or npm prefixes now required to avoid ambiguity between registries
• Package.json Integration
  • If project contains package.json, npm dependencies go there instead of deno.json
  • Support for dev dependencies using -D flag
• New Commands
  • deno install supports entry point flag for selective dependency installation
  • deno remove subcommand for quick dependency removal
• Lock File Improvements
  • New lock file format similar to pnpm
  • Better merge conflict resolution
  • Improved error messages with helpful hints

Permission System Overhaul

• Deno's security model: requires explicit permissions for file system, network access
• Default behavior: operations fail without proper permissions
• New error handling: special errors instead of OS-level errors
• Catchable errors within code for better error handling
• Various permission changes for file access, network access

Node.js Compatibility Improvements

• CommonJS Support Enhancement
  • Previously focused on ESM, now better CommonJS support
  • Can run .cjs files directly with deno run
  • Can import CommonJS files with .cjs extension
  • Support for requiring ES modules from CommonJS
  • Better error messages for CommonJS issues
• Node Modules Directory Handling
  • Three modes: none (default for Deno-first), auto, manual (default for package.json projects)
  • "Bring your own node_modules" functionality
  • Better compatibility with frameworks like Next.js, Remix, SvelteKit
• Node API Compatibility
  • Much more flushed out node crypto support
  • Async local storage more performant and reliable
  • Net.isPort and portfinder support
  • npm Puppeteer and Playwright more reliable

Breaking Changes

• Bundle Command Deprecated
  • Previously allowed creating standalone executables
  • Similar to Vercel's ncc but includes Deno runtime
  • New built-in bundler coming in future updates
• Import Assertions → Import Attributes
  • Keyword changed from assert to with
  • Proposal underwent major changes
  • Some browsers unshipped import assertions support

New Features

• Doc Tests
  • Type check and execute examples in JSDoc comments
  • deno test --doc ensures examples stay up to date
  • Can execute code blocks in markdown files
• TypeScript Updates
  • Ships with TypeScript built-in
  • New default settings: noImplicitOverride, useUnknownInCatchVariables
  • Built-in support for @types/node v22
  • Allow list for compiler options
• Web GPU APIs
  • Now stable, no longer require flags

CLI and Configuration Changes

• Escape commas in file names support
• Various permission system updates
• Better error messages throughout
• Improved backwards compatibility

JSR Package Registry

• New package registry built by Deno team
• Works with Node, Deno, and Bun
• Built-in TypeScript support
• Documentation generated from type definitions
• Goal to improve npm package management pain points