3 Apr 2024 · Software Engineering

    JavaScript’s Newest Framework: Bun. Will It Take Node’s Crown?

    11 min read
    This article is long. Download PDF to read it later.

    Huge thanks to Jarred Sumner for reviewing this post. It wouldn’t have been possible without his help.

    Bun is a new and ambitious JavaScript toolset and runtime. Early adopters have been reporting that Bun JavaScript is incredibly fast. So fast that it has been touted by some as a Node.js killer. Curious, I decided to check out Bun for myself and benchmark it against the competition.

    Is it as fast as people are saying? How stable is it? Is it really better than Node? And can I use it with continuous integration?

    What is Bun?

    Bun is the newest addition to the JavaScript family. It has been making waves that rival those made by Deno when it came out in 2018. Bun sits in the space between Node and Deno. Bun, like Deno, supports TypeScript out of the box and offers developer-friendly features such as top-level awaits and built-in Web APIs. But, unlike Deno, Bun is intended to be a drop-in replacement for Node, Webpack, Babel, Yarn, and PostCSS — all in one neat package.

    Plus, it has a really cute mascot

    Bun is released with an MIT and LGPL2 License (due to JavaScriptCore) and, at the time of writing, is on version v0.1.4.

    How does bun compare to Deno and Node?

    While Bun is inspired by Node and Deno, it is also clearly attempting to improve development experience and productivity by providing a batteries-included toolset.

    Bun JavaScript takes features from Deno, like shipping as a single binary and having native TypeScript support.

    TypeScript/TSX/JSX supportYesYes
    Single executableYesYes
    Built-in test runnerYes (in development)Yes
    Built-in Web APIs (fetch, WebSocket, etc.)YesYes
    Top-level awaitsYesYes
    npm compatibilityYesNo
    Node compatibilityYesPartial
    tsconfig.json supportYesNo
    WebAssembly supportYesYes
    Built-in linter & formatterNoYes
    Permission systemNoYes
    Package manifest formatpackage.jsonN/A
    Module supportES Modules, CommonJSES Modules
    LicenseMIT, LGPL2MIT
    JS EngineJavaScriptCoreV8
    LanguageZig, C++Rust, Tokio

    Compared to Node, Bun offers more features while striving to still be compatible:

    npm compatibilityYesYes
    Node compatibilityYes (beta)Yes
    Single binaryYesNo
    Built-in bundler & transpilerYesNo
    Native TypeScript supportYesNo
    Package manifest formatpackage.jsonpackage.json
    Lockfile formatBinaryJSON
    Native live-reloadYesNo
    Built-in .env, .toml supportYesNo
    Top-level AwaitsYesOnly on ES Modules
    JS EngineJavaScriptCoreV8
    LanguagesZig, C++C, C++
    LicenseMIT, LGPL2MIT, BSD

    Being in the beta stage, however, means that Bun still has some quirks:

    • Documentation is limited, but Bun’s Discord is very active and a great source of knowledge.
    • No native Windows support (works with WSL, though).
    • Bun can get stuck while installing packages, fetch is not reliable, and, although it never happened to me, Bun can occasionally segfault.
    • Bun is not 100% compatible with Node yet. Not every npm package works. Express, for instance, is not yet functional.
    • Publishing to the npm registry does not work.
    • Various breaking changes will occur before the APIs and the CLI are stable.

    Bun has a few distinct quality-of-life characteristics of its own:

    • Fast built-in sqlite3 module (MySQL and PostgreSQL are also planned).
    • Out-of-the-box .env, .toml, and CSS support (no extra loaders required).
    • Built-in framework support and optimizations for React and Next.js
    • Built-in Foreign Functions Interface (FFI) for low-level calls to ABI-supporting languages such as C, Rust, or Kotlin.
    • Option to copy errors as Markdown (for rapid sharing).

    Is it really that fast?

    Bun was born out of Jarred Sumner’s frustration with the speed, or lack thereof, of a language: “I’ve been so frustrated by how slow everything in JavaScript is. I know JavaScript can be a lot faster”. As a former frontend developer at Stripe, Jarred knows how a fast iteration cycle is essential for productivity.

    Developer experience matters. As a result, Bun’s speed is not limited to serving requests faster than other runtimes, but also means that it is faster at installing packages, running tests, bundling, and transpiling.

    Let’s run a few tests to see how Bun actually performs.

    Benchmarking Bun

    Bun’s homepage reports 3 and 4 times improved performance when compared against Deno and Node. Those are impressive numbers that I want to check for myself, so let’s run a few benchmarks across different categories:

    • Bun vs. npm as a package manager.
    • Bun vs. npm as a script runner.
    • Bun vs. npm for CI/CD workflows.
    • Bun vs. Node vs. Deno for copying large files.
    • Bun vs. Node vs. Deno for serving HTTP requests.

    In this instance, we’re going to benchmark:

    These are the tools I used for benchmarking:

    You can see the scripts used for each case here:

    I’ll try to compare Bun, Deno, and Node directly when possible. However, Deno was never intended as a drop-in replacement for Node, so it won’t be able to participate in all tests.

    Managing packages with Bun

    In this first test, we’ll compare how Bun JavaScript fares against npm for creating new projects. As you can see below, npm takes 49 seconds to create an empty React App.

    $ time npx create-react-app myapp

    Creating a new React app in /code/myapp.

    Installing packages. This might take a couple of minutes.
    Installing react, react-dom, and react-scripts with cra-template...

    added 1392 packages in 38s

    16.50s user 6.33s system 46% cpu 49.016 total

    Bun ships with the bun create command capable of doing the same:

    $ time bun create react myapp
    [package.json] Detected React - added "react-refresh"
    bun install v0.1.4
    🔍 Resolving [1/4]
    [29.00ms] git
    + react-refresh@0.10.0
    + typescript@4.7.4
    + react@18.2.0
    + react-dom@18.2.0
    + web-vitals@2.1.4
    8 packages installed [2.39s]
    2.48s user 0.30s system 66% cpu 4.160 total

    It takes Bun less than a second to complete the setup. That’s quite an improvement. But is this a valid comparison? Upon further inspection, we find that:

    • npm installed 1,392 packages and the node_modules size is 250 MB.
    • Bun only installed 8 packages, with a total size of 72 MB.

    We’re comparing apples to oranges here because Bun’s starter React template is slimmer. Surprisingly, it’s still quite usable for development. I can run bun dev to start hacking away immediately. Bun will also auto-reload on every change.

    Yet, Bun’s starter React cannot create a production build. For that, we’ll need to add react-scripts with:

    $ bun add react-scripts -d

    The new dependency installs 1,133 more packages, taking node_modules to a total of 298 MB. Now we’re in a better position for the comparison.

    After creating the new app 10 times with each tool, we have some numbers to compare.

    Package ManagerCreate React App (10 runs)
    npm17.937 ± 28.813
    Bun3.210 ± 5.430

    All tests were done with npm and bun caches warm, which explains why npm did much better the second time.

    A bar graphics comparing mean duration for bun and node.
    Bun is 6 times faster than npm for creating a complete React project.

    In this test Bun JavaScript looks pretty good: it is at least 6 times faster than npm. From time to time, however, Bun would lock up (a known issue). Also, npm would slow down considerably from time to time. I could not determine the cause for this.

    Adding and removing packages with Bun and npm

    Next, let’s test how long it takes npm and Bun to add and remove packages. I’ll use an npm-created React App as the testing ground.

    After removing and re-adding webpack 10 times with each tool, I got the following results:

    ToolAdd Webpack (10 runs)Remove We pack (10 runs)
    npm1900 ms4200 ms
    Bun100 ms200 ms

    Bar graphics comparing Add and Remove durations for Bun and Node.
    Bun is 20 times faster than npm. 

    The only catch is that Bun’s package management is not 100% compatible with npm:

    • Bun uses a binary lockfile instead of package-lock.json. But it can print out a Yarn-compatible JSON lockfile with bun install -y.
    • Bun does not install peer dependencies by default like npm. So you might end up with a different set of packages than expected in your node_modules folder.

    Bun as a task runner

    Unfortunately, Bun’s runtime component has not implemented enough Node APIs to do complex things such as building React projects or running end-to-end tests. Still, there is one area in which Bun can help us right now: as a replacement for npm run.

    The problem with npm is that it takes around 150 to 200ms to even start. It may not sound like a big deal, but when you’re running scripts frequently, you can feel that quarter of a second eating away at your productivity little by little.

    Bun does not have this start-up problem, so bun run test should be at least a few milliseconds faster than npm run test. We can confirm by running the same set of scripts 50 times and averaging the results:

    CommandMean elapsed time (50 runs)
    npm run test1.208 ± 0.011
    bun run test1.046 ± 0.030

    Bar graph comparing Bun and Node at Jest-based unit testing
    The difference is due to npm start-up time. The tests themselves are executed with Node on both cases.

    Copying large files

    In this test, I want to compare how each runtime handles copying large files, which is one area in which a lot of optimization effort was spent.

    I copied the same randomly-generated 1GB file with Bun, Deno, Node, and cp for the test. After 20 runs with each tool, the results were:

    ToolMean [s] (20 runs)Min [s]Max [s]Relative
    Bun1.222 ± 0.1581.0271.5561.00
    Deno1.276 ± 0.1321.1021.6141.04 ± 0.17
    cp1.802 ± 0.7140.4513.3041.47 ± 0.61
    Node4.003 ± 0.1453.8604.5903.27 ± 0.44

    Bar graph comparing file copy speed for Bun, Deno, cp and Node.
    Bun and Deno take the lead when copying large files.

    It seems Bun and Deno perform equally well, and both win over cp by almost 50%. Node is left far behind as it takes more than 3 times longer to complete the same task.

    HTTP Showdown: Bun vs Deno vs Node

    Bun’s JavaScriptruntime does include a working HTTP server, which presents a benchmarking opportunity to compare with Node and Deno. For the test, I’ll use Bun’s example scripts to drive the tests. I’ll generate and measure traffic with oha.

    The benchmark runs 2 million requests with a concurrency of 50. For all cases, the HTTP keepalive was enabled.

    RuntimeRPSTotal time (2M requests)
    Bun7096628.18 seconds
    Deno4040449.50 seconds
    Node3381459.14 seconds

    Bar graph comparing requests per second for Bun, Node and Deno.
    Bun is twice as fast as Node and 1.7 times faster than Deno for serving HTTP requests on my dev machine.

    Deno performed 19% better than Node, but Bun blew away the competition by performing twice as fast.

    Speeding up CI/CD with Bun

    We’ve confirmed that Bun can give you an edge on your development machine, but does it make sense to use it to accelerate CI/CD? This is a crucial aspect because the speed of your continuous integration pipeline is a deciding factor for a fast development cycle.

    I’ve configured two branches on Semaphore’s JavaScript demo project:

    • master runs all scripts with npm as originally designed.
    • The bun branch replaces npm with Bun. To be clear, we’re only using Bun as a task runner, not as a runtime. The test and build steps are still being executed by Node in both cases.

    Does Bun speed up CI/CD pipelines? After running both branches every ten minutes for five hours and picking 33 samples, the results are:

    RuntimeAverage pipeline run (33 runs)
    npm3 minutes 46 seconds
    Bun3 minutes

    Bar graph comparing pipeline durations for Bun- and Node-based workflows.
    Replacing npm with Bun speeds up my pipeline by 20%.

    While experimenting with driving CI/CD with Bun, I learned a few things:

    • Instead of caching the node_modules folder, it’s faster to save and restore Bun’s global cache located at $HOME/.bun/install/cache.
    • Bun ships with an experimental test runner, which is supposed to be much faster than Jest. Unfortunately, I wasn’t able to make it work. We’ll have to wait until the bun is out of the oven to try it (pun intended).
    • There’s a lot of potential for improvement. Once Bun runtime can replace Node, CI/CD speed might increase dramatically.


    Not only is Bun fast, it feels fast. It feels like you can do anything in under a second.

    Will Bun replace Node? It’s too early to say. When Deno came out, it certainly didn’t kill Node — but I don’t think that was the intention, as it was never meant as a Node replacement. But Bun JavaScript aims for compatibility, so it has a better chance. And, as we’ve seen, even at this early stage it can be a very powerful tool.

    Again, huge thanks to Jarred Sumner for his help on editing this article. Bun is a seriously cool project, so check it out on GitHub and collaborate if you can.

    This article is long. Download PDF to read it later.

    4 thoughts on “JavaScript’s Newest Framework: Bun. Will It Take Node’s Crown?

    1. hi,

      thx, a little note : your graphs are confusing. You should choose one way or the other not random one.

      Or you make bar representing more is better, or you represente more bar is less effective. For exemple :

      mb/s more is better
      s/mb less is better

      if every graph has a different meaning you confuse people. Having the same reading for all graph is better for presentation and understanding. You just have to reverse the unit if needed for the one than are reversed to present them in the same way.

      just my 2ct on presentation 🙂


    2. This is baseless, bun is far from as capable as Node or Deno. Yes node is slow, but taking a benchmark between Bun and the others when Bun isn’t even fully built to support the things that Deno and Node can do. I agree bun has made some good decisions with how they do things, like binary builds. But it’s still too early for benchmarks like this, bun could end up slower then Deno when it’s ready. At the end it may just become a battle between Zig and Rust, rather than Bun and Deno.

    3. Good article!!, Nice job!, just few things in bun vs deno table:
      – Typo on “No compatibility”
      – Deno supports tsconfig
      – I don’t find anything about bun & webassembly

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    Writen by:
    I picked up most of my skills during the years I worked at IBM. Was a DBA, developer, and cloud engineer for a time. After that, I went into freelancing, where I found the passion for writing. Now, I'm a full-time writer at Semaphore.