Fun with Express patterns

.md

Express patterns

Parametric modules

This pattern takes advantage of lexical scope in javascript, CommonJS modules, and object destructuring. It's a good way to share stateful resources, such as a db connection object, to middleware and detached routers in Express.

Basic setup

/app.js:

const express = require('express')
const app = express()

const errorReporter = require('./modules/errorReporter')
const mainRoute = require('./routes/main')

/* i'm using knex and postgres as an example,
 * but of course this will work with anything */
const db = require('knex')({
  client: 'pg',
  connection: {
    host: 'localhost',
    database: 'postgres',
  }
})

// all the stateful stuff other resources might need
const state = {
  db,
  errorReporter
}

app.use('/', mainRoute(state))

/routes/main.js:

const express = require('express')
const router = express.Router()

/** first we export a fn to act as a wrapper for our router.
  * as you can see, we destructure whatever we need out of the state
  * in this case, it's only the db */
module.exports = ({ db }) => {
  router.get('/', (req, res) => {
    // now my unwraped stateful deps are available in this module
  }
  
  return router
}