React w/ Service Worker & Push Notifications

Question

Some initial considerations:

"react": "^16.8.2",
"react-scripts": "2.1.5"

I have created a new react app and I need to implement Push Notifications. Following this tutorial, I was able to get up and running in 5 minutes, but now I have to implement the same strategy (kinda) into a react app.

The problem I am facing is that I am able to subscribe to the Notification API, but I'm not sure how to edit the service-worker.js file to add an event listener to catch the push event (Handle a Push Event chapter in the google guide)

Answer 1

Customizing your service worker with Create React App is possible, but could be quite difficult and hacky.

Out of the box, CRA uses Workbox GenerateSW webpack plugin to generate service-worker.js file, and you cannot inject any code to it (you could with CRA@1, not any more with since CRA@2)

You have several strategies, I'll start with the simplest one.

Solution 1: provide your own service-worker file

• in src/index.js enable service worker:

  // serviceWorker.unregister()
  serviceWorker.register()
  

• in src/serviceWorker.js register your custom file:

  // if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
  if ('serviceWorker' in navigator) {
  

  // const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
  const swUrl = `${process.env.PUBLIC_URL}/custom-service-worker.js`;
  

  You have to change the name cause when running dev server, CRA provides a mock for service-worker.js

• in public/ folder, create custom-service-worker.js file. Webpack will copy it as is in the build/ folder

Pros: quick, dirty win

Cons: your custom file is not processed with Webpack (no imports), and you must implement the network caching logic by yourself (assuming you want a PWA) since you're bypassing Workbox plugins

Solution 2: append your code to generated service-worker

There's a module for it: cra-append-sw. You're in charge to provide the appended code.

Pros: easy setup, takes advantages GenerateSW

Cons: appended code is processed with Babel/Webpack, but not using CRA's config (you could opt-out). Still use GenerateSW which handle network caching for you. Not sure it works when developing locally

Solution 3: use Workbox in custom service-worker file

• apply the first 2 steps of solution #1: change src/index.js and src/serviceWorker.js

• in src/ folder, create custom-service-worker.js file. It will be processed by Webpack, so you can use ES2016/TypeScript syntax and import modules

  /* eslint no-restricted-globals: "off" */
  import * as precaching from 'workbox-precaching'
  // your own imports
  
  if (self.__precacheManifest) {
  precaching.precacheAndRoute(self.__precacheManifest)
  }
  
  // your own code
  

• install react-app-rewire:

  • npm add --save-dev react-app-rewired
  • in package.json, in "scripts", replace react-scripts with react-app-rewired

• tweak webpack configuration: create config-overrides.js in root folder:

  const WebpackBeforeBuildPlugin = require('before-build-webpack')
  const WorkboxWebpackPlugin = require('workbox-webpack-plugin')
  const path = require('path')
  const merge = require('lodash.merge')
  const fs = require('fs')
  
  // from https://www.viget.com/articles/run-multiple-webpack-configs-sequentially/
  class WaitPlugin extends WebpackBeforeBuildPlugin {
  constructor(file, interval = 100, timeout = 60e3) {
   super(function(stats, callback) {
     const start = Date.now()
  
     function poll() {
       if (fs.existsSync(file)) {
         callback()
       } else if (Date.now() - start > timeout) {
         throw Error(`Couldn't access ${file} within ${timeout}s`)
       } else {
         setTimeout(poll, interval)
       }
     }
     poll()
   })
  }
  }
  
  const swOutputName = 'custom-service-worker.js'
  const workerSource = path.resolve(__dirname, 'src', swOutputName)
  
  module.exports = {
  webpack: (config, env) => {
   // we need 2 webpack configurations:
   // 1- for the service worker file.
   //    it needs to be processed by webpack (to include 3rd party modules), and the output must be a
   //    plain, single file, not injected in the HTML page
   const swConfig = merge({}, config, {
     name: 'service worker',
     entry: workerSource,
     output: {
       filename: swOutputName
     },
     optimization: {
       splitChunks: false,
       runtimeChunk: false
     }
   })
   delete swConfig.plugins
  
   // 2- for the main application.
   //    we'll reuse configuration from create-react-app, without a specific Workbox configuration,
   //    so it could inject workbox-precache module and the computed manifest into the BUILT service-worker.js file.
   //    this require to WAIT for the first configuration to be finished
   if (env === 'production') {
     const builtWorkerPath = path.resolve(config.output.path, swOutputName)
     config.name = 'main-application'
     config.plugins.push(
       new WorkboxWebpackPlugin.InjectManifest({
         swSrc: builtWorkerPath,
         swDest: swOutputName
       }),
       new WaitPlugin(builtWorkerPath)
     )
   }
  
   // remove Workbox service-worker.js generator
   const removed = config.plugins.findIndex(
     ({ constructor: { name } }) => name === 'GenerateSW'
   )
   if (removed !== -1) {
     config.plugins.splice(removed, 1)
   } 
  
   const result = [swConfig, config]
   // compatibility hack for CRA's build script to support multiple configurations
   // https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/scripts/build.js#L119
   result.output = { publicPath: config.output.publicPath }
   return result
  }
  }
  

Pros: you can use ES2016/TypeScript code in service-worker file. You still benefit from Workbox network caching facilities, with total control on it

Cons: complicated and fragile, because of the multiple configuration hack.

I've used the last solution, cause I needed both caching code from Workbox and some import in my service worker file.

react-app-rewire-workbox may help simplifying the Webpack configuration (the one for main app). To be tested.