Deno

Deno is a secure runtime for JavaScript and TypeScript, created by Ryan Dahl (the original creator of Node.js). It aims to provide a productive and secure scripting environment for the modern web.

Core Features

Built-in TypeScript Support

// No configuration needed for TypeScript
interface User {
  id: number;
  name: string;
}
 
async function getUser(): Promise<User> {
  const response = await fetch('https://api.example.com/user');
  return response.json();
}

Security First

Explicit Permissions

# Run with specific permissions
deno run --allow-net=api.example.com --allow-read=/tmp main.ts

Standard Library

// Using built-in modules
import { serve } from "https://deno.land/std/http/server.ts";
 
serve((req) => new Response("Hello, World!"), { port: 8000 });

Modern Features

URL Imports

import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
 
const add = (a: number, b: number): number => a + b;
 
Deno.test("add function", () => {
  assertEquals(add(2, 3), 5);
});

Web Platform APIs

// Using native fetch
async function getData() {
  const response = await fetch('https://api.example.com/data');
  const data = await response.json();
  return data;
}
 
// WebSocket support
const ws = new WebSocket('wss://ws.example.com');
ws.onmessage = (event) => {
  console.log('Received:', event.data);
};

Development Tools

Built-in Testing

Deno.test("async test", async () => {
  const response = await fetch("https://api.example.com");
  assertEquals(response.status, 200);
});

Code Formatting

# Format files
deno fmt
 
# Check formatting
deno fmt --check

Dependency Inspector

deno info main.ts

Performance

V8 Isolates

// Worker example
const worker = new Worker(new URL("./worker.ts", import.meta.url).href, {
  type: "module",
});
 
worker.postMessage({ type: "start", data: [1, 2, 3] });

Resource Management

// File system operations with permissions
const file = await Deno.open("example.txt", { write: true, create: true });
try {
  await file.write(new TextEncoder().encode("Hello, Deno!"));
} finally {
  file.close();
}

Package Management

Import Maps

{
  "imports": {
    "lodash/": "https://deno.land/x/lodash@4.17.15/",
    "testing/": "https://deno.land/std/testing/"
  }
}

Dependencies

// Import third-party modules
import { pick } from "https://deno.land/x/lodash@4.17.15/pick.js";
 
const obj = { a: 1, b: 2, c: 3 };
const picked = pick(obj, ['a', 'c']);

Deployment

Compile to Executable

deno compile --allow-net main.ts

Docker Integration

FROM denoland/deno:latest

WORKDIR /app

COPY . .

RUN deno cache main.ts

CMD ["deno", "run", "--allow-net", "main.ts"]

Best Practices

Use TypeScript

// Leverage type safety
type Config = {
  port: number;
  host: string;
};
 
function createServer(config: Config) {
  // Implementation
}

Implement Error Handling

try {
  const data = await Deno.readFile("config.json");
} catch (error) {
  if (error instanceof Deno.errors.NotFound) {
    console.error("Config file not found");
  } else {
    throw error;
  }
}

Additional Resources

Node.js Bun