changed webpack config

app/assets/javascripts/repo/lib/diff/diff_worker.js

 import { computeDiff } from './diff';
-// eslint-disable-next-line prefer-arrow-callback
-self.addEventListener('message', function diffWorker(e) {
+self.addEventListener('message', (e) => {
   const data = e.data;
   self.postMessage({

config/webpack.config.js

@@ -118,7 +118,10 @@ var config = {
       },
       {
         test: /\_worker\.js$/,
-        loader: 'worker-loader',
+        use: [
+          { loader: 'worker-loader' },
+          { loader: 'babel-loader' },
+        ],
       },
       {
         test: /\.(worker(\.min)?\.js|pdf|bmpr)$/,