Deno 1.0: A Fresh Take on Server-Side JavaScript

In May 2020, Ryan Dahl released Deno 1.0. If that name sounds familiar, it should. Ryan Dahl created Node.js. He walked away from the project years ago, and in a 2018 JSConf talk titled "10 Things I Regret About Node.js," he laid out everything he wished he had done differently. Deno is his answer to those regrets: a new JavaScript and TypeScript runtime built from scratch in Rust, with security, simplicity, and modern standards at the core.

I have been experimenting with Deno since the early preview builds, and 1.0 is the first version I would consider for actual projects. Here is what makes it interesting, where it falls short, and whether you should care.

Built-in TypeScript Support

This is the feature that grabbed my attention first. In Node.js, using TypeScript requires a build step. You install TypeScript, configure tsconfig.json, compile to JavaScript, and run the output. Or you use ts-node, which adds startup overhead. Either way, TypeScript is bolted on.

In Deno, TypeScript is a first-class citizen. You write a .ts file and run it directly:

// server.ts
var message: string = 'Hello from Deno';
console.log(message);

deno run server.ts

No compilation step. No tsconfig (though you can provide one for custom settings). Deno compiles TypeScript to JavaScript internally using a snapshot of the TypeScript compiler, caches the result, and runs it. The developer experience is noticeably smoother. You just write TypeScript and run it.

The Permission System

This is probably the most important architectural difference between Deno and Node. By default, a Deno script has zero access to the file system, network, or environment variables. You must explicitly grant permissions with flags:

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

# Allow reading files in a specific directory
deno run --allow-read=/tmp server.ts

# Allow network access only to specific domains
deno run --allow-net=api.github.com server.ts

# Allow everything (not recommended, but useful during development)
deno run -A server.ts

Think about what this means. If you install a malicious npm package in Node.js, it can read your file system, make network requests, and exfiltrate data. You would never know. In Deno, that same code would fail at runtime because it does not have the permissions it needs. This is a genuine security improvement, not just a checkbox feature.

The granularity is helpful too. You can allow network access to specific hosts and file system access to specific directories. A script that only needs to read from /data and talk to api.example.com gets exactly those permissions and nothing else.

URL-Based Imports

Node.js has node_modules, package.json, and npm. Deno has none of these. Instead, you import modules directly from URLs:

import { serve } from 'https://deno.land/[email protected]/http/server.ts';
import { format } from 'https://deno.land/[email protected]/datetime/mod.ts';

The first time you run the script, Deno downloads the modules and caches them locally. Subsequent runs use the cache. There is no node_modules directory (Ryan Dahl specifically called out node_modules as a regret in his JSConf talk). There is no centralized package registry that can go down and break everyone's CI pipelines.

In practice, you organize imports in a deps.ts file to centralize your dependency URLs:

// deps.ts
export { serve } from 'https://deno.land/[email protected]/http/server.ts';
export { format } from 'https://deno.land/[email protected]/datetime/mod.ts';
export { assertEquals } from 'https://deno.land/[email protected]/testing/asserts.ts';

// main.ts
import { serve } from './deps.ts';

var server = serve({ port: 8000 });
console.log('Server running on http://localhost:8000');

for await (var req of server) {
  req.respond({ body: 'Hello from Deno' });
}

The Standard Library

Deno ships with a reviewed standard library hosted at deno.land/std. It covers HTTP servers, file system operations, date formatting, UUID generation, testing utilities, and more. The quality is high because the Deno core team maintains it, and it is versioned so you can pin to specific releases.

Compare this with Node.js, where the built-in modules cover basics (fs, http, path) but you reach for npm packages for almost everything else. Need to parse command-line arguments? Install minimist. Need to make HTTP requests? Install node-fetch or axios. In Deno, many of these common needs are covered by the standard library out of the box.

Top-Level Await

In Node.js (at least until recent ESM support), using await required wrapping your code in an async function. The common pattern was:

// Node.js workaround
(async function() {
  var data = await fetchSomething();
  console.log(data);
})();

In Deno, every module is an ES module, and top-level await works natively:

// Just works in Deno
var response = await fetch('https://api.github.com/users/octocat');
var data = await response.json();
console.log(data.login);

This is a small thing, but it makes scripts and server entry points cleaner. No more async IIFE wrappers.

A Practical HTTP Server

Here is a more complete example showing a basic HTTP server with routing:

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

var server = serve({ port: 8000 });
console.log('Listening on http://localhost:8000');

for await (var req of server) {
  var url = new URL(req.url, 'http://localhost:8000');

  if (url.pathname === '/api/time') {
    req.respond({
      headers: new Headers({ 'content-type': 'application/json' }),
      body: JSON.stringify({ time: new Date().toISOString() })
    });
  } else if (url.pathname === '/api/hello') {
    var name = url.searchParams.get('name') || 'World';
    req.respond({
      headers: new Headers({ 'content-type': 'application/json' }),
      body: JSON.stringify({ message: 'Hello, ' + name })
    });
  } else {
    req.respond({
      status: 404,
      body: 'Not found'
    });
  }
}

Run it with deno run --allow-net server.ts, and you have a working API server. No npm install, no build step, no configuration files.

Deno vs Node: Where Each Wins

Deno wins on developer experience for new projects. Built-in TypeScript, built-in formatter (deno fmt), built-in linter (deno lint), built-in test runner (deno test), and a security model that makes sense. If you are starting a new script, CLI tool, or small service, Deno is genuinely pleasant to use.

Node wins on ecosystem. The npm registry has over a million packages. Deno's third-party module ecosystem is tiny by comparison. If your project depends on Express, Sequelize, Mongoose, or any of the thousands of battle-tested Node packages, you are staying on Node for now. Deno has a Node compatibility layer in the works, but as of 1.0, it is not mature enough for production use.

Node also wins on production tooling. PM2, clustering, monitoring, APM integrations, Docker base images optimized for Node, Kubernetes health check patterns. The Node production ecosystem is deep. Deno is still building this layer.

Should You Switch?

Not yet, at least not for production applications with complex dependency trees. But I am using Deno for scripts, internal tools, and greenfield microservices where I control the dependency graph. The developer experience is that good. The security model alone makes it worth considering for any code that handles untrusted input.

I think Deno's real impact will be forcing Node to improve. Node is already adopting ES modules, experimenting with permission models, and improving its built-in tooling. Competition makes everyone better. And if you are a JavaScript developer, having two serious runtime options is better than having one.