Bun Vs NodeJS – Is Bun Right Replacement For NodeJS?

Bun 1.0 is a new JavaScript runtime designed for modern JavaScript development and is likely to replace NodeJS completely.

It addresses the changing JavaScript ecosystem with frequent ECMAScript updates, TypeScript adoption, and the need for lighter runtimes as compared to NodeJS. 

“Bun uses JavaScriptCore, an Apple-developed engine for performance, and offers various APIs like DOM, WebStorage, and FetchAPI.“

Bun is a new runtime built from scratch to serve the modern JavaScript ecosystem as a NodeJS alternative in many ways. Wait… what? Do we really need more JS tools? Well,  the JavaScript space is completely different compared to the time when Node JS was first released. 

Since then, we get yearly new releases of the EcmaScript specification, TypeScript became the norm thanks to the improved developer experience and the popular tools like JSX are present in most web projects these days, and runtimes are forced to become lighter while computing is slowly moving to the edge. So the opportunity was there for JavaScript runtimes to get a facelift—Bun is planning to do just that. It is also worth mentioning that this is not a random little attempt to dethrone Node, and Oven, the company has massive support and funding to get it done. 

JavaScript Runtime 

Before talking about Bun’s toolkit, we will quickly clarify what exactly is a JS runtime. It all starts with an engine – the component that runs JavaScript code. V8 is the most popular option we all are familiar with, but Bun uses JavaScriptCore – a performance focused solution built by Apple for the Safari browser. Code is synchronously processed, with function calls placed on the stack and object memory is allocated in the heap. This engine can’t do a lot of useful things on its own, so the runtime also offers various useful APIs. 

The browser’s DOM API used to build UIs, the WebStorage API for data persistence or the FetchAPI which performs HTTP calls. These APIs can then trigger events which will place callbacks or in the Task and Microtask queues. The final piece of the runtime puzzle is a non-blocking event loop which constantly motors the queues. Basically, whenever the call stack is empty, it will move workloads from the queue to the stack. 

This architecture is implemented from scratch in Bun, using Zig, JavaScriptCore and very efficient system calls under the hood. Zig is a general-purpose language which combines the performance benefits of a low level language with a great developer experience. So all these implementation details result in better performance on both start times and memory management. So if we combine it with the promise of exceptional speed, and we have a real competitor for NodeJS. 

Bun Features In A Nutshell

Here are some of Bun’s core competencies – its capability to be a drop-in replacement for Node.js it’s due solely to the provided native implementation of hundreds of Node.JS and WebAPIs modules. You will still use a package.json file to manage NPM dependencies in a node_modules directory, but installing these dependencies is way faster compared to the Node world. And, since we are talking about speed, this is a big focus in the Bun world, and they are taking a lot of pride in the results. Of course, benchmarks are not always that objective, but I still think some of the numbers here are rather impressive. 

The Bun ecosystem already enjoys various libraries and tools tailored for this new runtime. Elysia is one of the fastest web frameworks in this space promising end-to-end type safety and an outstanding developer experience. In the terminal we can bootstrap a new project via bun create. Then, in the source directory, you’ll find an index.ts file where we could easily define routes for our API. the features you would expect from a web framework ranging from route management to state and extensibility via plugins. 

We have talked about Typescript instead of JavaScript. That’s because Bun acknowledges the importance of TypeScript in modern web development and offers first class support for it. 

Compatibility of Bun 

Bun aims to be compatible with Node, which relied on Common JS modules for a long time, so these are also supported while not recommended. Another nice little feature which will come in handy when building large apps with various build scripts is that Bun provides extensive Macros support. These are leveraging ECMAscript’s import attribute (still in stage 3) and allow us to run code while bundling. Here is the example of using Macros with Bun:

We can run code at bundle-time. Here’s a basic example:

// version.macro.ts
import { createMacro } from 'bun/macro';

export const getVersion = createMacro(() => {
  return `Version: ${process.env.APP_VERSION}`;
});

We can use this macro in our code like shown here:

// app.tsx
import { getVersion } from './version.macro';

const version = getVersion();

// ...rest of our code

To give you an idea about some Macro use cases, imagine your app is being tested by your QA team, and you want to make sure they are able to identify the current version of your app. We run a new process in Macros, get the last commit, then simply import the function as a macro and output its result in JSX. 

Besides the runtime, Bun offers a powerful debugger and test utilities enjoying the same performance and speed gains you should be used to by now. This talk about runtimes wouldn’t be complete without giving any credit to Deno which is another popular JS runtime created by Ryan Dahl – the same guy who came up with Node JS. Deno is actually an entire platform offering a full stack framework, native key value storage and even a deployment platform.

It is built from scratch using Zig, JavaScriptCore, and efficient system calls, resulting in improved performance in terms of startup times and memory management.

Bun can serve as a drop-in replacement for Node.js, offering native implementation of many NodeJS and WebAPIs modules, faster dependency installation, and sole focus on speed. 

Some practical uses of Bun 1.0

We can create Bun server to listen to GET requests and send responses:

// index.ts
import { createServer, IncomingMessage, ServerResponse } from 'bun/http';

const server = createServer((req: IncomingMessage, res: ServerResponse) => {
  res.end('Hello, Bun!');
});

server.listen(8000);

Using TypeScript and JSX:

Bun offers first-class support for TypeScript and JSX. You can write your code in TypeScript and use JSX for building user interfaces without additional setup:

// example.tsx
import { h } from 'bun/jsx-runtime';

const element = <div>Hello, Bun JSX!</div>;

Only widespread use of Bun would show in the future how far it could replace NodeJS. It’s a great resource for coding and has tons of use-cases. We have mentioned just a few here.