Deno provides a secure JavaScript/TypeScript runtime. After building applications with Deno, here’s how to use it effectively.

What is Deno?

Deno features:

  • Secure by default - Explicit permissions
  • TypeScript - Built-in support
  • Standard library - No external dependencies
  • Modern - ES modules, async/await

Installation

# Install Deno
curl -fsSL https://deno.land/install.sh | sh

# Or with Homebrew
brew install deno

# Verify
deno --version

Basic Usage

Hello World

// hello.ts
console.log('Hello, Deno!');

// Run
deno run hello.ts

HTTP Server

// server.ts
Deno.serve((req) => {
    return new Response('Hello, Deno!', {
        headers: { 'content-type': 'text/plain' },
    });
}, { port: 8000 });

Permissions

Explicit Permissions

# Network permission
deno run --allow-net server.ts

# File system permission
deno run --allow-read --allow-write script.ts

# All permissions
deno run --allow-all script.ts

Permission Prompts

// Request permission
const status = await Deno.permissions.request({ name: 'net', host: 'example.com' });
if (status.state === 'granted') {
    // Use network
}

Standard Library

HTTP Server

import { serve } from 'https://deno.land/std@0.200.0/http/server.ts';

serve((req) => {
    return new Response('Hello from Deno!');
}, { port: 8000 });

File Operations

// Read file
const text = await Deno.readTextFile('./data.txt');

// Write file
await Deno.writeTextFile('./output.txt', 'Hello, Deno!');

// Read directory
for await (const dirEntry of Deno.readDir('./')) {
    console.log(dirEntry.name);
}

Web APIs

Fetch

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

WebSocket

const ws = new WebSocket('ws://localhost:8080');

ws.onopen = () => {
    ws.send('Hello, Server!');
};

ws.onmessage = (event) => {
    console.log('Received:', event.data);
};

Modules

Import from URL

// Import from URL
import { serve } from 'https://deno.land/std@0.200.0/http/server.ts';

// Import from local file
import { helper } from './helper.ts';

Import Maps

// import_map.json
{
    "imports": {
        "http/": "https://deno.land/std@0.200.0/http/",
        "fs/": "https://deno.land/std@0.200.0/fs/"
    }
}

// Use import map
import { serve } from 'http/server.ts';

// Run with import map
deno run --import-map=import_map.json app.ts

Testing

Deno Test

// test.ts
import { assertEquals } from 'https://deno.land/std@0.200.0/testing/asserts.ts';

Deno.test('should add numbers', () => {
    assertEquals(1 + 1, 2);
});

# Run tests
deno test

Best Practices

  1. Use permissions - Explicit and minimal
  2. TypeScript - Leverage type safety
  3. Standard library - Use built-in modules
  4. Import maps - Manage dependencies
  5. Testing - Write tests
  6. Formatting - Use deno fmt
  7. Linting - Use deno lint
  8. Documentation - Clear code

Conclusion

Deno provides:

  • Secure runtime
  • TypeScript support
  • Modern features
  • Standard library

Use Deno for secure, modern applications. The patterns shown here work for production.

Deno secure runtime from March 2021, covering permissions, standard library, and modern JavaScript features.