Deno Cheatsheet

Quick Start

``bash # Run a script deno run main.ts

# Run with network access deno run --allow-net main.ts

# Watch mode — auto-restart on changes deno run --watch main.ts

# Format code deno fmt

# Run tests deno test

# Start REPL deno repl

# Evaluate inline code deno eval 'console.log("hello deno")' `

Install & Setup

`bash deno --version # Show version info deno upgrade # Upgrade to latest deno upgrade --version 2.0.0 # Upgrade/downgrade to specific version deno info # Show cache and module resolution info `

Basic Usage

`bash deno run main.ts # Run a file deno run --watch main.ts # Watch mode (auto-restart on file changes) deno eval 'console.log("hi")' # Run inline code deno repl # Start interactive REPL `

Script Management

`bash deno compile --allow-read main.ts # Compile to standalone binary deno compile --target x86_64-unknown-linux-gnu main.ts # Cross-compile deno compile --output dist/cli main.ts # Custom output name deno install -g --allow-net --allow-read https://deno.land/std/http/file_server.ts # Install global script deno uninstall file_server # Uninstall global script deno task dev # Run task from deno.json deno task --watch test # Task watch mode `

Permissions

`bash deno run --allow-read main.ts # Allow file system read deno run --allow-write main.ts # Allow file system write deno run --allow-net main.ts # Allow network access deno run --allow-env main.ts # Allow env variable access deno run --allow-all main.ts # Grant all permissions deno run --allow-read=/data --allow-write=/tmp main.ts # Scope to paths deno run --allow-net --deny-net=api.example.com main.ts # Deny specific hosts `

Package Management

`bash deno add @std/assert # Add JSR dependency deno add npm:express # Add npm dependency deno remove @std/assert # Remove a dependency deno publish # Publish module to JSR deno cache main.ts # Cache remote module dependencies `

Testing & Lint

`bash deno test # Run all tests deno test --watch # Run tests in watch mode deno test --coverage # Run tests with coverage collection deno bench # Run benchmarks deno lint # Lint code for style & errors deno fmt # Format code (built-in formatter) deno check main.ts # Type-check without executing `

Advanced

`bash deno doc mod.ts # Generate documentation deno doc --json mod.ts # Output docs in JSON format deno jupyter --install # Start Jupyter kernel (experimental) deno serve main.ts # Start HTTP server (Fetch API) deno run --v8-flags=--max-old-space-size=2048 main.ts # Set V8 memory deno run --inspect-brk main.ts # Debug (paused at first statement) `

FAQ

### How do I configure Deno?

Create a deno.json or deno.jsonc in your project root. It supports tasks, imports (import map), compiler options, lint/fmt settings, and publish configuration. Example:

`json { "tasks": { "dev": "deno run --watch --allow-net main.ts", "test": "deno test --coverage" }, "imports": { "express": "npm:express@^5.0.0" } } `

### How do I use Web APIs in Deno?

Deno implements browser-compatible Web APIs: fetch, Request, Response, WebSocket, Console, setTimeout, URL, Blob, File, FormData, TextEncoder, ReadableStream, and more. No polyfills needed — they Just Work.

`typescript // Fetch example (needs --allow-net) const res = await fetch('https://api.example.com'); const data = await res.json(); `

### How do I debug Deno scripts?

Use --inspect or --inspect-brk to start the V8 inspector, then connect Chrome DevTools or VS Code debugger:

`bash deno run --inspect-brk main.ts # Open chrome://inspect in Chrome ``