main.js

... 

failedPostListener = () => {
  navigator.serviceWorker.addEventListener('message', event => {
    var form = document.getElementById('form');

    // Alert displays the message sent from our service worker
    alert(event.data.msg);

    // Assuming personal-details database have been created with
    // form_data object store.
    // We simply write to form_data.
    idb.open('personal-details', 1).then(function(db) {
      const tx = db.transaction('form_data', 'readwrite');
      const store = tx.objectStore('form_data');
      store.put({name: `${form[0].value}`});
    })

  });
}