🎴 Cromo

A tiny, fast & simple file-based router server for Bun 🧄

Table of Contents

• Set up
• Router
• Handlers
• Middlewares
• Start server
• Context object

Server set up

To get started with Cromo, you need to download the package using Bun:

bun add cromo

Next, import and initialize Cromo in your code:

import { Cromo } from 'cromo'

const cromo = new Cromo({
  dir: './src/api'  // default: './api'
  port: 5000        // default: Bun.env.PORT || 3000
})

Router usage

Cromo utilizes a file-based router system. By default, the router folder is named api, but you can change it by passing the dir option during initialization:

// File structure example
├── api
│   ├── hello
│   │   ├── [world]
│   │   │   └── index.ts
│   └── user
│       ├── [name].ts
│       └── index.ts
└── index.ts

Handlers usage

Inside the router files, you can write HTTP method handlers:

// api/hello/[world]/index.ts
import type { CromoContext, CromoHandler } from 'cromo'

// handler for GET method
export const GET: CromoHandler = (context) => {
  const { world } = context.params
  return Response.redirect(`https://google.com/search?q=${world}`)
}

// default handler is called if there is no specific handler for the method
export default (context: CromoContext): Response => {
  return Response.json(null, 404)
}

Middlewares

There are three ways to add middlewares in Cromo:

1. Using setMiddleware: Simply call setMiddleware to add an array of middlewares to the server.

// index.ts
cromo.setMiddleware([
  (context, next) => {
    console.log("middlewares called")
    return next(context)
  },
  ...
])

2. Declaring middlewares const: Declare an array of middlewares in the router files as middlewares const.

// api/user/index.ts
import type { CromoHandler, CromoMiddleware } from 'cromo'

export const GET: CromoHandler = ({ responseInit }) => {
  return Response.json({ name: 'John' }, responseInit)
}

export const middlewares: CromoMiddleware[] = [
  ({ responseInit }, next) => {
    responseInit.headers = {
      'Access-Control-Allow-Origin': '*'
    }
    return next(context)
  }
]

3. Declaring [METHOD]_middlewares const: Declare an array of middlewares in the router files as [METHOD]_middlewares const to apply middlewares to a specific method.

// api/user/[name].ts
import type { CromoHandler, CromoMiddleware } from 'cromo'

export const POST: CromoHandler = ({ params, responseInit }) => {
  const { name } = params
  return Response.json({ name }, responseInit)
}

export const POST_middlewares: CromoMiddleware[] = [
  ({ responseInit }, next) => {
    responseInit.headers = {
      'Access-Control-Allow-Origin': '*'
    }
    return next(context)
  }
]

Start the server

By default, Cromo will listen to port Bun.env.PORT, and if it is not set, it will listen to port 3000. However, you can change it by passing the port option during initialization.

Here is an example of starting the server:

cromo.start(port => {
  console.log(`Listening on port ${port}`)
})

Context object

In Cromo, we use the context object to pass data between middlewares and handlers. It contains basic Web API objects like Request, URL, ResponseInit, and some useful properties like matchedRoute, body, params, query.

import { MatchedRoute } from 'bun'

export interface CromoContext {
  // request objects
  request: Request
  url: URL
  matchedRoute: MatchedRoute
  body: unknown
  params: Record<string, string>
  query: Record<string, string>
  // response objects
  responseInit: ResponseInit
}