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Engineering

February 05, 2025

Engineering

Bun vs. Node.js: Performance and use cases in cloud apps

Ben Force

February 05, 2025

Ben Force

On the surface, Node.js and Bun may seem similar—they're both server-side JavaScript runtimes using a JavaScript engine from a web browser. But a closer look reveals differing priorities. Render hosts services with both the Node.js and Bun runtimes, and customers have seen performance improvements when switching to Bun. In this article, we'll take a look at the strengths and weaknesses of Bun and Node.js. Stick around—things get interesting when we discuss deploying applications to the cloud.

What is Bun?

Bun is a modern JavaScript runtime. Its primary focus is on speed and efficiency, which it implements through its choice of the JavaScriptCore engine that Apple built for its Safari browser. Bun also comes with a built-in tool set so you can quickly get started building projects.

What is Node.js?

Node.js is the original server-side JavaScript runtime. It uses the V8 engine from Google Chrome for its JavaScript engine. Because a lot of services rely on it, Node.js's development is focused on stability.

Bun's strengths

Bun is a JavaScript runtime newer than Node.js and has distinguished itself in a few ways.

Built-in vs. external tooling

Bun comes with a bunch of tools out of the box. You don't have to run a separate transpiler, bundler, and test runner; Bun combines these tools into one. Beyond getting you up and running quickly, the tools are written in a compiled language, which means they're very fast and don't have a lot of resource overhead.

Bundler

One of Bun's built-in tools is its bundler. The bundler has an API similar to esbuild, but according to their benchmarks, Bun's bundler is slightly faster. If you want to compare Bun with some other bundlers yourself, take a look at js-bundler-benchmark on GitHub, which provides a collection of sample projects with various bundler configurations for comparison. Here's a chart showing some results from a js-bundler-benchmark GitHub repository:

Transpiler

Bun can run TypeScript files directly, which means you won't need to add ts-node as a development dependency. The transpiler also supports TypeScript's path mappings out of the box so you don't have to configure an extra plugin. Bun transpiles TypeScript files by stripping types, meaning it doesn't provide type safety—similar to how esbuild works. To ensure type errors are caught, Bun's documentation recommends running tsc to catch type errors.

Test runner

Testing is another area where Bun simplifies things. It provides a built-in test runner that is Jest-compatible. While it isn't quite a drop-in replacement for Jest, it's very similar. If you want to see if a certain feature has been implemented, there's an open issue tracking what's currently missing from Jest. As far as performance goes, Bun's benchmarks claim it can run 266 React Server-Side Rendering (SSR) tests faster than Jest can print its version number. This is an illustration of the overhead in startup times that Jest requires since it's JavaScript code that needs to be interpreted. For an apples-to-apples comparison, a simple test suite can be used to benchmark Bun against Jest. For a test suite with only two tests (one that always passes and one that always fails), Jest takes an average of 40.34 times longer to run and uses 3.33 times more memory than Bun. Below is a chart showing the results of benchmarking a simple test suite with both Jest and Bun:

Hot reload

Bun's hot reloading works similarly to nodemon—it monitors your source files, and when it detects a change, it updates your running process. The difference is that nodemon resets the whole process, but Bun just updates its internal copy of the changed module. This means it's faster and doesn't lose its state. To illustrate the difference, run the following code with nodemon:

// src/counter.js
module.exports.counter = (value) => {
  console.info(`Counts: ${value}`);
  return value + 1;
}

// src/index.js
const { counter } = require('./counter');

globalThis.currentValue ??= 0;

const main = async () => {
  while(true) {
    const newValue = counter(globalThis.currentValue);
    globalThis.currentValue = newValue;

    await new Promise((resolve) => setTimeout(resolve, 1000));

    if (globalThis.currentValue !== newValue) {
      break;
    }
  }
};

main().then(() => null);

If you run npx nodemon ./src/index.js, then change src/counter.js and save it, you'll see the count gets reset every time you make a code change. The picture below shows an example of this happening:

Now, if you run bun --hot ./src/index.js and do the same change in src/counter.js, when you save the file, you'll see the output clear and then pick up with the same global count being displayed:

As you can see, the app is restarting on code changes, but the global count state stays the same.

Web API access

Bun has built-in support for modern Web APIs like WebSockets and fetch. This means you can develop common libraries to be shared between your frontend and backend services without having to add the bloat of a polyfill to get it to work.

Performance and startup speed

The JavaScriptCore engine used by Bun is built for phones and laptops, so it's optimized to use less battery power, which means less memory consumption. In contrast, the V8 runtime used by Node.js optimizes runtime, but that takes more memory. To show the difference this runtime selection makes, benchmarking the same "Hello World" script executed with Bun and Node.js shows 1.31 times more memory usage and 1.87 times longer runtimes for Node.js:

Comparison of Bun and Node running a "Hello World" benchmark

If performance is your primary goal, it's important that you run benchmarks for your specific use case and platform to compare Node.js and Bun. In general, Bun will have faster startup and response times and will be able to handle a higher number of requests with a given amount of memory. There are, however, some platforms that have optimized their Node.js runtime over the years to the point that its performance is neck-and-neck with Bun in some cases. The image below shows the results from benchmarks on a Lambda function that returns a static string. You can see that Bun's average response time only beats Node.js's by 6 ms:

Results of AWS Lambda response time benchmarks

Best fit use cases

With Bun's strengths in mind, let's take a look at a few ways you can apply them to your projects.

Low-latency servers

Bun's defining feature is its speed—if you have a service that needs to send responses in real time, Bun is a great choice. A quick benchmark sending 1,000 requests per second to a REST API returning a static value shows that Node.js takes 4.73 times as long to respond to a request:

Servers with limited resources

Bun's use of the JavaScriptCore engine positions it perfectly to run in environments with low resources. Since it's designed to run on everything from an iPhone to an Apple TV, it needs to work reliably on devices with limited memory. This means Bun will work great if you want to save on the server instance that you're using by giving it less memory. It'll also easily run on a Raspberry Pi for IoT development.

Quick prototypes

If you need to get a proof of concept built, you can't go wrong with all of Bun's built-in tools. They're fast, and you don't have to download them.

Node.js strengths

Now that you've seen Bun's strengths, let's take a look at the strengths of the industry standard: Node.js.

Community and ecosystem support

While Bun has a lot of built-in tools and APIs, Node.js is adding more of its own. Node.js was the first server-side JavaScript runtime introduced to the world in 2009, and since that time, there have been countless third-party libraries created to address different issues. As of 2022, there were over two million packages available on npm. Those packages represent not just libraries but tools like test runners and linters to help your development experience. In addition to the libraries and tools available, there are countless tutorials, courses, and answers available on Stack Overflow. Currently, there are almost 500,000 upvoted answers tagged with "node.js" on Stack Overflow. This means if you can't find something that's already written, you have countless resources to use when building it yourself.

Stability and production readiness

Since big companies like PayPal and agencies like NASA are using Node.js to build mission-critical applications, it has to be reliable. That's why every October, Node.js creates a release labeled LTS, or long-term support. That version will receive critical bug fixes for thirty months, which means you can stick with a version of Node.js for about two years before you have to migrate to a new version.

Error handling and debugging

A lot of developers have written and fixed bugs in Node.js applications over the years. Because of this and the V8 engine's inspector protocol, you get a solid step-through debugging experience in a lot of IDEs. You can easily execute your code one line at a time in your IDE until you've found the source of a bug. While Bun does provide a WebKit inspector protocol to enable step-through debugging on your application, it isn't as widely supported as V8's inspector protocol.

Deployment flexibility and platform support

Node.js is supported by a wide range of platforms. For instance, when AWS Lambda was launched in 2014, Node.js 0.10 was one of the first runtimes available. Since then, it's been added to countless platforms, and there's an official Docker image so you can run your Node.js application anywhere that a Docker container can be deployed.

Best fit use cases

As you can see, Node.js's advantages vary quite a bit in comparison to Bun, so its ideal use cases are also different.

Legacy applications

If you have a project that uses a lot of third-party libraries, you'll probably need to stick with Node.js for the time being. A lot of libraries published to npm make use of Node.js's built-in libraries, which aren't fully supported by Bun yet. If you don't want to rewrite those libraries, sticking with Node.js is the safest option.

Mission-critical applications

If you have a server that needs to guarantee a certain level of availability, then the stability of Node.js is what you need. Node.js has a long history and has earned its stability over the years through experience. It also provides LTS releases (on a predictable schedule) that get bug fixes for a long time, so you can migrate to newer, stable versions as you have time.

Small teams

If you have a small team and must handle deploying the infrastructure yourself, then the wide support for Node.js is a big advantage. Most service providers will have documentation on how to get a Node.js application deployed, and if they don't, then you can probably find a tutorial or answer on Stack Overflow.

When to pick Bun

If your project's primary goal is speed, then Bun is the best option. Because of its built-in tools, it's faster than Node.js in both runtime and development time. It's also a great choice if you're running it in an environment with limited resources. If you've written a modern, Web API-driven project that has minimal dependencies, then Bun will really shine. Bun's runtime is significantly faster than Node.js's for both startup and the number of requests that it can handle per second. This is great for real-time applications when latency is the primary concern. For developer speed, Bun's built-in tooling means you don't need to run npm install for a bunch of packages before starting work on a project. The developer tools are also fast since they aren't written in JavaScript.

When to pick Node.js

If you have an application that needs to be completely stable, then Node.js should be your go-to. Node's LTS releases and its years of experience in providing stability should be taken into account. If you have a really complex project or a project that requires a lot of third-party libraries, then Node.js is a better runtime choice. Your codebase more than likely requires some of Node.js's built-in libraries, which may not be fully implemented in Bun. Also, Bun's libraries aren't as battle-tested as Node.js's, and you may find more edge cases where there's unpredictable behavior. Finally, you may need to use Node.js instead of Bun if your target platform or CI/CD system doesn't support Bun. Also, if you're working on a small team without cloud or DevOps support, you may not want to go through the work of getting Bun set up when Node.js is a simpler option. Here's a quick chart summarizing the capabilities of Bun and Node.js:

	Bun	Node.js
Stability	Has a 1.x release, but less tested	Mature, provides LTS releases
TypeScript support	Built-in	Experimental
Bundler	Built-in	Third-party
Hot reloading	Hot reload and full restart	Full restart
Serverless functions	Similar	Similar
Memory usage	Lower	Higher
REST response times	Faster	Slower

Conclusion

If you're choosing between Node.js and Bun, consider Node.js if you have complex projects that require a lot of third-party libraries. However, Bun is the preferred choice for lightweight, low-latency projects. Like any new tool that you use, you'll need to run experiments to make sure it's the right choice. Try out both Node.js and Bun and see which one works better for your use case. To simplify your experimentation, use Render. It supports both runtimes natively and provides a sample project to get started deploying Bun projects. Our blog includes a real-world use case of Bun substantially speeding up a GitHub pipeline's runtime.