You can never get too complacent with the JavaScript eco-system, no sooner do you start to feel comfortable than something else becomes the new hotness, this time it’s bun. Bun is a JavaScript runtime, pretty much analogous to Node.js, so basically a potential replacement for Node.js.

Setting things up

The Installation page gives details on setting up for various OS’s, Windows is not well supported at the moment (i.e. experimental release), but as I love devcontainers in VSCode, we’ll just set up a devcontainer to use the docker image.

• Create a folder for your (yes we’re going to do it) hello world app, mine’s named hello-world
• Create folder named .devcontainer (for more info. see my post Visual Code with vscontainers)
• Create a file in .devcontainer named devcontainer.json and put the following code in it

  {
    "image": "oven/bun",
    "forwardPorts": [3000]
  }
  

Now open Visual Code on the folder hello-world (or whatever you named it) and VS Code will hopefully ask if you want to open the folder as a devcontainer, obviously say yes and it’ll set up the docker image for you and then you’ll be working in a devcontainer with bun.

Is it working?

If you carried the steps above (or installed by one of the other means) we now want to check bun is working. From your terminal either on the devcontainer or any terminal if you installed it on your machine or container, run the command

bun

You should see a list of commands etc. If not, check through your installation and in the case of the devcontainer make sure you’re using the terminal in VS Code and it’s showing your root folder of the docker image.

Getting Started

Hopefully everything is running, so we need to create something, so run

bun init

Then fill in the options, mine are using all the defaults, but I’ll then them below anyway

• package name hello-world
• entry point index.ts

and that’s all there’s is so it. Bun will create and index.ts file, .gitignore, tsconfig.json, package.json and READEME.md. The index.ts looks like this

console.log("Hello via Bun!");

Let’s run this using

bun run index.ts

As you’d expect we’re seeing Hello via Bun! in our terminal window.

I want a server!

Most, if not all my work with Node.js was writing server based code, so let’s take the example from the Bun Quick Start page and fire up a little server app.

const server = Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Hello World from the server");
  },
});

console.log(`Listening on http://localhost:${server.port} ...`);

We’re using port 3000 which we also have listed in our devcontainer.json within forwardPorts. So running index.ts from bun will start the server on port 3000 and VS Code (in my case) will ask if I wish to open the browser for that port. If you’re using a different method then simply open your browser with URL http://localhost:3000/.

We can ofcourse put scripts into our package.json, to save us some typing, for example adding

"scripts": {
    "start": "bun run index.ts"
  },

Now we can use the command

bun run start

Everything else should pretty much work as Node.js, but it’s reported that bun (which essentially also includes package management tooling) is quite a bit faster than npm and yarn, also it includes hot reload out of the box, i.e. we don’t need to use Nodemon. It automatically transpiles TypeScript and JSX. So it’s very much an “all in one” solution to Node.js style development.

So that’s a really quick run through and a reminder to myself how to get bun up and running as quickly as possible.