Deno 2.0: The Modern JavaScript Runtime That's Ready for Production

Deno 2.0 marks a significant milestone in the JavaScript ecosystem. Created by Ryan Dahl (the original creator of Node.js), Deno addresses many of Node’s design regrets while introducing modern features that developers have been requesting for years. With version 2.0, Deno is finally production-ready with full npm compatibility.

Why Deno 2.0 Matters

Feature	Deno 2.0	Node.js
TypeScript	Native, zero config	Requires setup
Security	Permissions by default	Full access
Package manager	Built-in	npm/yarn/pnpm
Formatting	Built-in (deno fmt)	Prettier needed
Linting	Built-in (deno lint)	ESLint needed
Testing	Built-in (deno test)	Jest/Vitest needed
npm compatibility	Full support	Native

Getting Started

Installation

# macOS/Linux
curl -fsSL https://deno.land/install.sh | sh

# Windows (PowerShell)
irm https://deno.land/install.ps1 | iex

# Homebrew
brew install deno

# Verify installation
deno --version

Your First Deno Script

// hello.ts - No configuration needed!
const name: string = "World";
console.log(`Hello, ${name}!`);

// Run with:
// deno run hello.ts

Key Features

1. Native TypeScript Support

No tsconfig.json, no ts-node, no compilation step:

// api.ts
interface User {
  id: number;
  name: string;
  email: string;
}

async function fetchUser(id: number): Promise<User> {
  const response = await fetch(`https://api.example.com/users/${id}`);
  return response.json();
}

const user = await fetchUser(1);
console.log(user.name);

deno run --allow-net api.ts

2. Security by Default

Deno runs in a sandbox. You must explicitly grant permissions:

# No permissions - script can't do much
deno run script.ts

# Allow network access
deno run --allow-net script.ts

# Allow file system read
deno run --allow-read script.ts

# Allow specific paths
deno run --allow-read=/tmp --allow-write=/tmp script.ts

# Allow environment variables
deno run --allow-env script.ts

# Allow all (not recommended for production)
deno run -A script.ts

3. Full npm Compatibility (Deno 2.0)

// Use npm packages directly
import express from "npm:express@4";
import lodash from "npm:lodash";

// Or use import maps (deno.json)
import chalk from "chalk";  // mapped in deno.json

deno.json:

{
  "imports": {
    "chalk": "npm:chalk@5",
    "lodash": "npm:lodash@4",
    "@/": "./src/"
  }
}

4. Built-in Tooling

# Format code (like Prettier)
deno fmt

# Lint code (like ESLint)
deno lint

# Run tests
deno test

# Bundle for browser
deno bundle mod.ts bundle.js

# Generate documentation
deno doc mod.ts

# Check types without running
deno check mod.ts

# Compile to executable
deno compile --allow-net server.ts

Building a REST API

// server.ts
import { Application, Router } from "https://deno.land/x/oak@v12.6.1/mod.ts";

interface Todo {
  id: number;
  title: string;
  completed: boolean;
}

const todos: Todo[] = [
  { id: 1, title: "Learn Deno", completed: false },
  { id: 2, title: "Build API", completed: false },
];

const router = new Router();

router
  .get("/api/todos", (ctx) => {
    ctx.response.body = todos;
  })
  .get("/api/todos/:id", (ctx) => {
    const id = Number(ctx.params.id);
    const todo = todos.find((t) => t.id === id);
    if (todo) {
      ctx.response.body = todo;
    } else {
      ctx.response.status = 404;
      ctx.response.body = { error: "Todo not found" };
    }
  })
  .post("/api/todos", async (ctx) => {
    const body = await ctx.request.body().value;
    const todo: Todo = {
      id: todos.length + 1,
      title: body.title,
      completed: false,
    };
    todos.push(todo);
    ctx.response.status = 201;
    ctx.response.body = todo;
  });

const app = new Application();
app.use(router.routes());
app.use(router.allowedMethods());

console.log("Server running on http://localhost:8000");
await app.listen({ port: 8000 });

deno run --allow-net server.ts

Testing in Deno

// math.ts
export function add(a: number, b: number): number {
  return a + b;
}

export function multiply(a: number, b: number): number {
  return a * b;
}

// math_test.ts
import { assertEquals } from "https://deno.land/std@0.208.0/assert/mod.ts";
import { add, multiply } from "./math.ts";

Deno.test("add function", () => {
  assertEquals(add(2, 3), 5);
  assertEquals(add(-1, 1), 0);
});

Deno.test("multiply function", () => {
  assertEquals(multiply(2, 3), 6);
  assertEquals(multiply(0, 5), 0);
});

Deno.test("async operation", async () => {
  const result = await Promise.resolve(42);
  assertEquals(result, 42);
});

deno test

Migrating from Node.js

Package.json to deno.json

Before (package.json):

{
  "dependencies": {
    "express": "^4.18.0",
    "lodash": "^4.17.0"
  },
  "scripts": {
    "start": "node index.js",
    "test": "jest"
  }
}

After (deno.json):

{
  "imports": {
    "express": "npm:express@4",
    "lodash": "npm:lodash@4"
  },
  "tasks": {
    "start": "deno run --allow-net index.ts",
    "test": "deno test"
  }
}

Common Patterns

// Node.js
const fs = require('fs');
const data = fs.readFileSync('file.txt', 'utf8');

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

// Node.js
const path = require('path');
const fullPath = path.join(__dirname, 'file.txt');

// Deno
const fullPath = new URL('./file.txt', import.meta.url).pathname;

Deno Deploy

Deploy serverless functions globally:

// main.ts
Deno.serve((req: Request) => {
  const url = new URL(req.url);

  if (url.pathname === "/api/hello") {
    return Response.json({ message: "Hello from Deno Deploy!" });
  }

  return new Response("Not Found", { status: 404 });
});

# Deploy to Deno Deploy
deno deploy

Performance Comparison

Benchmark	Deno 2.0	Node.js 20	Bun
HTTP requests/sec	120k	95k	150k
Cold start	30ms	50ms	20ms
TypeScript compile	0ms	500ms+	0ms
Memory usage	Low	Medium	Low

When to Use Deno

Choose Deno for:

• New TypeScript projects
• Security-sensitive applications
• Serverless/edge functions
• Scripts and tooling
• Learning modern JavaScript

Stick with Node.js for:

• Existing large codebases
• Heavy npm ecosystem dependency
• Team familiarity
• Specific framework requirements

Summary

Aspect	Details
Version	2.0 (Production ready)
TypeScript	Native, zero config
Security	Sandboxed by default
npm support	Full compatibility
Tooling	All-in-one (fmt, lint, test)
Best for	New projects, TypeScript, security

Deno 2.0 represents a mature, production-ready alternative to Node.js. With full npm compatibility, native TypeScript support, and built-in tooling, it’s never been easier to give Deno a try. For new projects, especially those prioritizing security and TypeScript, Deno 2.0 is a compelling choice.