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The Evolution of JavaScript Runtimes: From Node.js to Bun and Beyond

The Evolution of JavaScript Runtimes: From Node.js to Bun and Beyond

There's something almost poetic about JavaScript's transformation over the past fifteen years. What started as a hastily-created browser scripting language—famously written in just 10 days by Brendan Eich back in 1995—has become one of the most versatile languages in software development. But this isn't really a story about JavaScript itself. It's about the runtimes that liberated it from the browser and turned it into something we could actually build servers, APIs, and full applications with.

When JavaScript Was Stuck in the Browser

For more than a decade after its creation, JavaScript had one job: make web pages slightly more interactive. You could validate a form before submission. Maybe add a dropdown menu if you were feeling fancy. That was about it.

// Classic browser-only JavaScript (circa 2000)
function validateForm() {
  var email = document.getElementById('email').value;
  if (email.indexOf('@') === -1) {
    alert('Please enter a valid email');
    return false;
  }
  return true;
}

Sure, there were attempts to break JavaScript out of its cage. Rhino came along in 1997, and Netscape Enterprise Server tried even earlier. But none of them really took off. The performance wasn't there, the tooling was rough, and honestly, nobody was that excited about running JavaScript on servers when we had perfectly good languages like PHP, Perl, and Java already doing that job.

Then Ryan Dahl Had an Idea

It's 2009. Chrome has just released V8, their blazing-fast JavaScript engine. Ryan Dahl is frustrated with the limitations of existing server technologies, particularly Apache's approach to handling concurrent connections. He's thinking about how most web servers block while waiting for I/O operations, which seems wasteful. What if you could have a server that just... didn't wait around?

So he takes V8, wraps it with an event-driven, non-blocking I/O model, and presents Node.js at JSConf EU. The demo is simple—a web server in just a few lines of code:

var http = require('http');

http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
}).listen(8080);

console.log('Server running at http://localhost:8080/');

That's it. No XML configuration files, no complicated setup. Just JavaScript doing server things. The developer community went wild.

But Node.js wasn't just about making servers easy. It introduced this whole philosophy of non-blocking operations that made it incredibly efficient at handling lots of concurrent connections. While other servers would spawn a new thread for each connection (expensive!), Node.js could juggle thousands of connections with a single thread, thanks to its event loop.

The timing was perfect too. Frontend developers were already getting more sophisticated with JavaScript frameworks, and now they could use the same language on the backend. "JavaScript everywhere" wasn't just a marketing slogan—it meant you could share code, switch between frontend and backend more easily, and hire engineers who could work across the entire stack.

NPM Changed Everything

Here's the thing though: Node.js might have just been an interesting technical curiosity if not for NPM. Isaac Schlueter created the Node Package Manager in 2010, and it solved a problem that seems obvious in retrospect but was actually pretty revolutionary—making it dead simple to share and use other people's code.

npm install express

That one command would download Express, a web framework, along with all its dependencies, and set everything up for you. Compare that to manually downloading libraries, managing versions, and dealing with dependency conflicts in other languages, and you can see why NPM became a killer feature.

By 2023, NPM hosted over 2 million packages. Think about that for a second. TWO MILLION. It's the largest software registry in the world. Want to parse dates? There's a package. Need to handle file uploads? Package. Want to build a complete REST API? Multiple packages competing for your attention.

This explosion of shared code meant that building with Node.js was fast. Really fast. You could scaffold a complete application in an afternoon using packages that thousands of other developers had already battle-tested.

// Express.js made REST APIs trivial
const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.json({ message: 'Hello World' });
});

app.listen(3000);

Soon, Node.js was powering everything from simple APIs to Netflix's entire UI infrastructure. Companies like PayPal reported that Node.js applications were built twice as fast with fewer people, and performed better to boot. The ecosystem exploded with frameworks and tools: Express, Socket.io for real-time communication, Meteor for full-stack apps, and even Electron, which let you build desktop apps with web technologies (Slack, VS Code, and Discord are all Electron apps).

But Node.js Had Problems

As Node.js matured and more people started using it for serious production applications, some cracks started showing. Don't get me wrong—Node.js is still massively popular and isn't going anywhere. But there were design decisions that, in hindsight, created real pain points.

Remember "callback hell"? If you wrote Node.js between 2010 and 2014, you remember. Everything was asynchronous, and everything used callbacks, which meant your code quickly turned into a pyramid of doom:

fs.readFile('file1.txt', 'utf8', function(err, data1) {
  if (err) return handleError(err);
  fs.readFile('file2.txt', 'utf8', function(err, data2) {
    if (err) return handleError(err);
    fs.readFile('file3.txt', 'utf8', function(err, data3) {
      if (err) return handleError(err);
      processData(data1, data2, data3, function(err, result) {
        if (err) return handleError(err);
        console.log(result);
      });
    });
  });
});

Look at that indentation! Each asynchronous operation nested inside the previous one. Debugging this was a nightmare. Following the logic was worse. We called it "callback hell" for good reason.

Promises helped when they landed in 2015, and async/await in 2017 made async code almost pleasant to write. But these were band-aids on a fundamental design choice made years earlier.

Then there was the module system mess. Node.js committed to CommonJS modules early on—you know, the require() and module.exports syntax. Meanwhile, JavaScript itself evolved and standardized on ES Modules with import and export. So now you had two competing module systems, and developers had to understand both, often in the same codebase. Node.js eventually added ES Module support in 2019, but by then, the ecosystem was deeply fractured.

The security model was another issue that became obvious once people started thinking about it. Any script you ran, any package you installed, had complete access to your entire file system and network. Want to read /etc/passwd and send it somewhere? No problem! This led to some spectacular supply chain attacks where malicious packages would steal environment variables or cryptocurrency wallets.

And then there was the tooling complexity. Want to use TypeScript? You'll need ts-node or tsx. Want to bundle your code? That's webpack. Want to lint? ESLint. Format? Prettier. Watch for changes? Nodemon. Building a production-ready Node.js app meant wrestling with a dozen different tools, each with their own configuration files.

Ryan Dahl's Do-Over

In 2018, something interesting happened. Ryan Dahl, the guy who created Node.js, gave a talk called "10 Things I Regret About Node.js." He was remarkably candid about the design decisions that seemed reasonable at the time but caused problems later. And then he announced Deno—essentially, "what if I could build Node.js again, knowing what I know now?"

Deno flipped the script on several of Node.js's core assumptions. The most dramatic? Security by default. In Deno, scripts have no access to the file system, network, or environment variables unless you explicitly grant permission. Want to read a file? You need to run your script with --allow-read. Want to make network requests? That's --allow-net.

// This will fail with PermissionDenied
Deno.readTextFile('./secret.txt');

// You must run: deno run --allow-read script.ts

Deno also went all-in on TypeScript from day one. Not "TypeScript is supported if you set up the right tooling," but "TypeScript just works out of the box." No configuration, no build step. Just write TypeScript and run it.

The module system was another complete rethink. No npm, no node_modules folder that mysteriously balloons to gigabytes. Instead, Deno imports directly from URLs:

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

serve((req) => new Response("Hello World"));

The first time you run this, Deno fetches and caches the module. After that, it's available offline. It's weird at first, but it grows on you. No package.json, no installing dependencies, no wondering which version of a package is actually installed.

Deno also shipped with built-in tooling. Want to format your code? deno fmt. Lint it? deno lint. Run tests? deno test. Bundle for production? deno bundle. It's all there, and it all works together without configuration files.

But here's the brutal truth: Deno struggled with adoption. Despite its technical superiority in many ways, it wasn't compatible with the millions of NPM packages that developers relied on. The ecosystem was tiny in comparison. And migrating an existing Node.js codebase? Forget about it—you'd basically be rewriting from scratch.

Deno's team eventually added NPM compatibility, but by then, the momentum had stalled. The corporate world had invested heavily in Node.js infrastructure, and "technically better" doesn't always win against "already works."

Enter Bun: The Performance Maniac

Just when the JavaScript runtime landscape seemed settled—Node.js dominant, Deno interesting but niche—Jarred Sumner dropped Bun in 2022 with a simple promise: it's faster than everything else. Not a little faster. A LOT faster.

Bun made some bold technical choices. While Node.js and Deno both use Google's V8 engine, Bun uses JavaScriptCore from WebKit. V8 is highly optimized for peak performance, but JavaScriptCore focuses on fast startup times. For developer tooling and CLIs, that startup time matters a lot.

Bun is also written in Zig, a relatively new systems programming language that lets you get close to the metal while still having modern safety features. The result? Bun is absurdly fast.

How fast? Bun can handle around 260,000 HTTP requests per second in benchmarks, compared to Node.js's 30,000. That's not a typo. And bun install is routinely 10-20x faster than npm install. The first time you run it and watch your entire dependency tree install in two seconds, it feels like magic.

But speed isn't Bun's only trick. It's also fully compatible with Node.js, meaning you can often just replace node with bun in your scripts and everything works. TypeScript runs directly without any configuration. JSX works out of the box. And it ships with SQLite built-in, so you can have a database without installing anything.

// A complete API with database, no external dependencies
import { Database } from "bun:sqlite";

const db = new Database("app.db");
db.run(`
  CREATE TABLE IF NOT EXISTS todos (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    text TEXT NOT NULL,
    completed BOOLEAN DEFAULT 0
  )
`);

export default {
  port: 3000,
  
  async fetch(req: Request) {
    const url = new URL(req.url);
    
    if (url.pathname === "/todos" && req.method === "GET") {
      const todos = db.query("SELECT * FROM todos").all();
      return Response.json(todos);
    }
    
    if (url.pathname === "/todos" && req.method === "POST") {
      const { text } = await req.json();
      const result = db.run("INSERT INTO todos (text) VALUES (?)", [text]);
      return Response.json({ id: result.lastInsertRowid, text });
    }
    
    if (url.pathname.startsWith("/todos/") && req.method === "PATCH") {
      const id = url.pathname.split("/")[2];
      const { completed } = await req.json();
      db.run("UPDATE todos SET completed = ? WHERE id = ?", [completed, id]);
      return Response.json({ success: true });
    }
    
    return new Response("Not Found", { status: 404 });
  },
};

The catch? Bun is young. Really young. It's still rapidly evolving, which means things break between versions sometimes. The ecosystem is stable for common use cases, but venture into less-traveled territory and you might hit bugs. For production systems handling critical workloads, that's a hard sell. But for side projects, CLIs, and newer applications? Bun is an absolute joy to work with.

The Bigger Picture

What's fascinating about this runtime evolution is how each one reflects different priorities and lessons learned. Node.js proved that JavaScript could be taken seriously on the server and prioritized ecosystem growth above all else. Deno said "wait, what about security and modern standards?" Bun looked at everything and asked "but what if it was just... faster?"

There are other players too. CloudFlare Workers runs JavaScript at the edge using V8 isolates, making it possible to run code globally distributed with near-zero cold start times. QuickJS is tiny and embeddable, perfect for IoT devices. GraalVM can run JavaScript at near-native speeds and interoperate with Java, Python, and other languages.

The competition has been incredibly healthy for the ecosystem. Node.js itself has gotten faster and added better features in response to alternatives. Deno pushed the importance of security and modern tooling. Bun's speed made everyone question their performance assumptions.

So Which One Should You Use?

Here's the honest answer: it depends, and that's actually a good thing.

Node.js still makes sense for most production applications, especially in enterprise environments. The ecosystem is massive, the tooling is mature, and you can hire engineers who already know it. If you're maintaining existing applications or need maximum stability, Node.js isn't going anywhere.

Deno is excellent if you're starting fresh and care deeply about security and modern practices. The permission system alone makes it worth considering for applications that handle sensitive data. The built-in tooling means less configuration and fewer dependencies. It's particularly good for CLIs and edge computing scenarios.

Bun is the exciting newcomer that you'll want to try on side projects first. The speed is addictive—once you experience bun install completing in seconds, going back to npm feels painful. If you're building something new and can tolerate some rough edges, Bun offers the best developer experience available right now. Just maybe don't bet the company on it yet.

The truth is, we're in a golden age for JavaScript developers. The language itself has matured tremendously with features like async/await, optional chaining, and nullish coalescing. The runtimes give us choices based on our specific needs. And the competition keeps pushing everyone to improve.

What's Next?

The runtime landscape will keep evolving. WebAssembly integration is getting better, letting us run highly optimized code alongside JavaScript. Edge computing is pushing runtimes to be smaller and faster to start. The WinterCG (Web-interoperable Runtimes Community Group) is working to standardize APIs across runtimes, so code written for one will work on others.

We're also seeing runtimes specialized for specific use cases. Vercel's edge runtime is optimized for serverless functions. Deno Deploy focuses on instant global distribution. Bun keeps pushing performance boundaries.

The future probably doesn't involve one runtime dominating the way Node.js has. Instead, we'll likely use different runtimes for different purposes, choosing the right tool for each job. Your API server might run on Node.js for stability, your edge functions on Deno Deploy for security and speed, and your CLI tools built with Bun for the incredible developer experience.

And honestly? That's pretty exciting. JavaScript started as a quick hack to make web pages slightly interactive. Now it's running servers, powering desktop applications, controlling IoT devices, and executing at the edge of CDN networks globally. The runtime wars aren't about one winner—they're about pushing the boundaries of what's possible with JavaScript as a platform.

The kid who was stuck in the browser has grown up and learned to run anywhere. And it keeps getting faster, safer, and more capable with each passing year.