web worker - fetch data and store them into browser extension db

Question

I want to use a web worker to speed up some images and data fetch operations. I've created the worker and it's working as expected but I have a problem in my browser extension background file. I've implemented nedb-promises to store the data after that the extension is installed and the data are fetched to use them later into the extension. The problem is that I'm unable to save the fetched data that are passed from the worker. The database field I'm creating when the data are received will be always empty. How I can fix this?

import nedb from 'nedb-promises';

const db = nedb.create({ filename: 'cache', autoload: true });
const worker = new Worker('js/worker.js');

browser.runtime.onInstalled.addListener( (details) => {
  console.log(details);
  db.insert({ imagesData: null});
  worker.postMessage('fetchImages');
});

browser.runtime.onStartup.addListener( () => {
  db.findOne({ imagesData: {$exists: true } })
  .then( (data) => {
    console.log(data);
    if( data ){
      browser.runtime.sendMessage(data);
    }else{
      worker.postMessage('fetchImages');
    }
  });
});

worker.onmessage = async (e) => {
  console.log(e);
  const data = e.data;
  console.log(data);
  const update = await db.update({ imagesData: {$exists: true} }, { $set: { imagesData: data } });
  browser.runtime.sendMessage(data);
}

browser.tabs.onCreated.addListener( () => {
  db.findOne({ imagesData: {$exists: true} })
  .then( (data) => {
    console.log(data);
    browser.runtime.sendMessage(data.imagesData);
  });
  console.log('tab created');
});