Deno Technology Intelligence

What is Deno?

Deno is a secure runtime for JavaScript and TypeScript built on V8 and Rust. It addresses design issues Ryan Dahl identified in Node.js, offering built-in TypeScript support, a security-first approach with permissions, and modern features like top-level await.

Created by Ryan Dahl (original creator of Node.js) and announced in 2018, Deno represents a rethinking of server-side JavaScript. It eliminates node_modules and package.json, instead using URL imports like browsers. Deno includes built-in tools for testing, formatting, and linting, providing a more complete runtime experience out of the box.

Key Features

Security

• Permissions: Explicit access grants required
• Sandboxed: No file/network access by default
• Granular Control: --allow-read, --allow-net, etc.
• Prompt Mode: Interactive permission requests

TypeScript Native

• Built-in: No configuration needed
• Type Checking: Optional with --check flag
• JSX Support: React and Preact compatible
• Fast Compilation: SWC-based

Module System

• URL Imports: Import from any URL
• ESM Only: No CommonJS
• Import Maps: Alias management
• npm Compatibility: npm: specifier support

Built-in Tools

• deno fmt - Code formatter
• deno lint - Linter
• deno test - Test runner
• deno compile - Create executables

Use Cases

Edge Functions

Deno Deploy provides globally distributed serverless functions. The runtime's fast startup and small footprint make it ideal for edge computing with sub-millisecond cold starts.

Secure Scripting

System administrators write automation scripts with Deno's permission system. Scripts can't access unauthorized files or network resources, reducing security risks from untrusted code.

API Development

Developers build REST and GraphQL APIs with Fresh or Oak frameworks. TypeScript-first development catches errors early, and the standard library provides HTTP server primitives.

Single Executables

Teams distribute CLI tools as single binaries with deno compile. No runtime installation required—users run the executable directly on any supported platform.

TypeScript Projects

Teams start TypeScript projects without build configuration. Deno runs .ts files directly, eliminating tsconfig.json setup for simple projects.

Learning and Prototyping

Developers prototype ideas quickly without npm initialization. URL imports pull dependencies directly, and the built-in REPL supports TypeScript.

Code Examples

HTTP Server

// server.ts
Deno.serve({ port: 3000 }, (req: Request) => {
    const url = new URL(req.url);

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

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

// Run: deno run --allow-net server.ts

File Operations

// read-write.ts

// Read file
const content = await Deno.readTextFile("./data.json");
const data = JSON.parse(content);

// Write file
await Deno.writeTextFile(
    "./output.json",
    JSON.stringify(data, null, 2)
);

// Read directory
for await (const entry of Deno.readDir("./src")) {
    console.log(entry.name, entry.isFile);
}

// Run: deno run --allow-read --allow-write read-write.ts

URL Imports and Import Maps

// Direct URL import
import { serve } from "https://deno.land/[email protected]/http/server.ts";

// Or use import map (deno.json)
// {
//   "imports": {
//     "std/": "https://deno.land/[email protected]/",
//     "oak": "https://deno.land/x/[email protected]/mod.ts"
//   }
// }

import { Application } from "oak";

const app = new Application();
app.use((ctx) => {
    ctx.response.body = "Hello from Oak!";
});

await app.listen({ port: 8000 });

Testing

// math_test.ts
import { assertEquals } from "https://deno.land/[email protected]/assert/mod.ts";

function add(a: number, b: number): number {
    return a + b;
}

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

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

// Run: deno test --allow-net

Comparison and Ecosystem

Deno vs Node.js

• TypeScript: Deno native, Node requires setup
• Security: Deno sandboxed, Node unrestricted
• Modules: Deno URL/npm:, Node npm only
• Ecosystem: Node much larger

Deno vs Bun

• Focus: Deno security, Bun speed
• TypeScript: Both native support
• npm: Both support npm packages
• Tooling: Deno more built-in tools

Ecosystem

• deno.land/std: Standard library
• Fresh: Web framework (Islands architecture)
• Oak: Middleware framework
• Deno Deploy: Edge hosting platform

Strengths

• Security-first design
• TypeScript without configuration
• Modern, Web-standard APIs
• Built-in development tools

Considerations

• Smaller ecosystem than Node.js
• npm compatibility still maturing
• Some Node.js patterns don't translate
• Learning curve for permission system