Work Around main.«hash».js missing from service-worker.js

build-precache-fixup.js

#!/usr/bin/env node
// Works around issue described at
// https://github.com/facebook/create-react-app/issues/3574#issuecomment-410141752
// To use, add this as “&& ./build-precache-fixup.js” to
// package.json/scripts.build.

const crypto = require('crypto');
const fs = require('fs');
const path = require('path');

const assetManifest = require('./build/asset-manifest.json');
const mainUri = assetManifest['main.js'];

const serviceWorkerJsPath = path.join('build', 'service-worker.js');
const serviceWorkerJs = fs.readFileSync(serviceWorkerJsPath, 'utf-8');
const matches = /(precacheConfig=)(\[\[.*?\]\])/.exec(serviceWorkerJs);
if (!matches || !matches[2]) {
  throw new Error(`Unable to locate precacheConfig= in ${serviceWorkerJsPath}`);
}
const dataStringPrefix = matches[1];
const dataString = matches[2];
// Check if main is there. If it is, skip.
const data = JSON.parse(dataString);
const hasMain = !!data.filter(entry => {
  return entry[0] === mainUri;
}).length;
if (!hasMain) {
  const mainJsMd5Hash = (() => {
    const hash = crypto.createHash('md5');
    hash.update(fs.readFileSync(path.join('build', mainUri)));
    return hash.digest('hex');
  })();
  data.push([mainUri, mainJsMd5Hash]);
}
const newDataString = JSON.stringify(data);
// Splice into service-worker.js
const newServiceWorkerJs = serviceWorkerJs.substring(0, matches.index)
      + dataStringPrefix
      + newDataString
      + serviceWorkerJs.substring(matches.index + matches[0].length);
const serviceWorkerJsTmpPath = serviceWorkerJsPath + '#';
fs.writeFileSync(serviceWorkerJsTmpPath, newServiceWorkerJs);
fs.renameSync(serviceWorkerJsTmpPath, serviceWorkerJsPath);