@artsy/express-reloadable

When developing a Node app it's common to rely on tools like node-dev or nodemon to make the development process more rapid by automatically restarting the server instance on file-change. What express-reloadable does is listen for source-code changes within a subset of your app and, scanning Node's internal module cache, clears the require call if found. This tricks Node into thinking the module has not yet been loaded, effectively hot-swapping out your code without a full restart. Crazy-fast development speed!

(Disclaimer: While this works for most of our use-cases, this is effectively a hack and hasn't been tested in all environments. Your milage may vary :)

How it works:

• express-reloadable is called with a path to an app, which it then mounts
• When source-code within that folder / app changes an internal lookup is made to Node, scanning its require cache for the changed file
• If found, it is cleared internally via delete require.cache[id]
• When the browser is reloaded express-reloadable executes a callback that re-requires the code and changes are instantly available.

Installation:

yarn add @artsy/express-reloadable

Example:

The below example assumes that the folders /api and /client exist, and that each contain an index file that exports a mountable express.js route.

import express from 'express'
import { createReloadable, isDevelopment } from '@artsy/express-reloadable'

const app = express()

if (isDevelopment) {

  // Pass in app and current `require` context
  const reloadAndMount = createReloadable(app, require)

  // Note that if you need to mount an app at a particular root (`/api`), pass
  // in `mountPoint` as an option.
  app.use('/api', reloadAndMount(path.resolve(__dirname, 'api'), {
    mountPoint: '/api'
  }))

  // Otherwise, just pass in the path to the express app and everything is taken care of
  reloadAndMount(path.resolve(__dirname, 'client'))
} else {
  app.use('/api', require('./api')
  app.use(require('./client')
}

app.listen(3000, () => {
  console.log(`Listening on port 3000`)
})

Thanks:

This package was heavily inspired by @glenjamin's ultimate-hot-loading-example.