spec/fixtures/pages/service-worker/index.html

<script>
  const ipcRenderer = require('electron').ipcRenderer;
  navigator.serviceWorker.register('service-worker.js', {scope: './'}).then(function() {
    if (navigator.serviceWorker.controller) {
      var xhr = new XMLHttpRequest();
      xhr.open('GET', 'http://dummy/echo');
      xhr.setRequestHeader('X-Mock-Response', 'yes');
      xhr.addEventListener('load', function() {
        ipcRenderer.send('response', xhr.responseText);
      });
      xhr.send();
    } else {
      ipcRenderer.send('reload');
    }
  }).catch(function(error) {
    ipcRenderer.send('error', `${error.message}\n${error.stack}`);
  })
</script>