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https://github.com/artsy/express-reloadable

Automatically hot-swap Express server code without the restart
https://github.com/artsy/express-reloadable

developer-tools express hot-swap

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Automatically hot-swap Express server code without the restart

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README 

        
# @artsy/express-reloadable



When developing a Node app it's common to rely on tools like [`node-dev`](https://github.com/fgnass/node-dev) or [`nodemon`](https://github.com/remy/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. Additionally, when the `watchModules` option is passed, `express-reloadable` will listen for changes to NPM module code and reload on change. Useful when working with `yarn link` across packages / repos. Crazy-fast development speed!



> **Disclaimer**: While this works for most of our use-cases, this is an example of "`require hacking"` and hasn't been tested in all environments. Your mileage 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 a new request is made `express-reloadable` executes a callback that re-requires the code and changes are instantly available.



**Installation**:



```sh

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.



```js

import express from 'express'

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



const app = express()



if (isDevelopment) {



  // Pass in `app` and current `require` context

  const mountAndReload = createReloadable(app, require)



  // Pass in the path to an express sub-app and everything is taken care of

  mountAndReload(path.resolve(__dirname, './client'))



  // Full example:

  app.use('/api', mountAndReload(path.resolve(__dirname, './api')), {



    // If you need to mount an app at a particular root (`/api`), pass in

    // `mountPoint` as an option.

    mountPoint: '/api',



    // Or if you're using `yarn link` (or npm) to symlink external dependencies

    // during dev, pass in an array of modules to watch. Changes made internally

    // will be instantly available in the app. Additionally, using something like 

    // `glob`, other modules outside of express route path can be passed.

    watchModules: [

      '@artsy/reaction',

      '@artsy/artsy-xapp'

    ]

  }))



  // If prod, mount apps like normal

} else {

  app.use('/api', require('./api')

  app.use(require('./client')

}



app.listen(3000, () => {

  console.log(`Listening on port 3000`)

})

```



**Troubleshooting**:



> Help! I've mounted my app using reloadable but I'm not seeing any changes?



For the utility to work you need to a) ensure that `NODE_ENV=development` (for safety) and b) the path to your app is absolute:



```js

// Incorrect

app.use(reloadAndMount('./path/to/app'))



// Correct 

app.use(reloadAndMount(path.resolve(__dirname, 'path/to/app')))

```



**Thanks**:



This package was heavily inspired by @glenjamin's [ultimate-hot-loading-example](https://github.com/glenjamin/ultimate-hot-reloading-example).