Accessing an indexedDB from code inside a Blob

Question

Accessing an indexedDB from code inside a Blob

First I have to explain the scenario:

Kiosk internet app with CHROMIUM showing LOCAL webs. That is, the web server is not installed. Chrome always shows "file: ///" pages.
Reason: Sometimes the computer might be offline (network problems, wifi range ...).
Requirement: We want to use Google Analytics. When the computer is ONLINE, the system sends an HTTP request to GA normally. When OFFLINE, we want to store the http request in indexedDB.
Using a worker completing a task every X seconds, we check the internet connection. If successful, the worker receives http requests saved in indexedDB and sent to Google Analytics.

We have achieved all steps but one: accesing indexedDB of javascript code inside the Blob .

The reason for using js Worker inside Blob is because Chrome does not allow access to javascript files when the script is local (File: ///). This is a small example of a worker inside a Blob that receives an indexedDb every 3 seconds. For example, the example works fine in Firefox. But in Chrome this exception is thrown when code is executed, accessing indexedDb from BLOB code:

Unhandled rejection: OpenFailedError: SecurityError Failed to execute 'open' in 'IDBFactory': Access to the indexed database API in this context is denied.

<html>
  <head>
      <title>Example error blob and indexeddb</title>
  </head>

  <body>
    <p>This example demostrate that javascript code inside a Blob can't access indexedDb in Chrome.</p>
    <p>Click 'Start WebWorker' to create a Worker inside a Blob. This worker tries to insert some<br>
    data into a database created in 'startWorker()' function.</p>
    <button type="button" onclick="startWorker()" id="btnStart">
        Start WebWorker
    </button>
    <button type="button" onclick="stopWorker()" id="btnStop">
        Stop WebWorker
    </button>


  <!-- FOR LOGGING INFO PURPOSES -->
  <p id="demo"></p>

  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>


  <!-- TRICK !! Declare this block of type 'javascript/worker' or something non-standard.
      Later we can create on the fly javascript executable code
      using a Blob (see 'window.onload' function later on this file)
  -->
  <script id="worker" type="javascript/worker">

        var started = false;
        var timer;

        onmessage = function (event)
        {
            var orden = event.data.toString();

            switch (orden)
            {
                case 'start':
                    start();
                    break;
                case 'stop':
                    stop();
                    break;
                default:
                    notRecognized(orden);
                    break;
            }
        }

        function start()
        {
            if( ! started)
            {
              timer = setInterval(function(){ job() }, 3000);
              started = true;
            }
        }

        function stop()
        {
            if(started)
            {
                clearInterval(timer);
                started = false;
            }
        }

        //Executed each 3 seconds (see start() )
        function job()
        {
          // Open the database -> ERROR!! Uncaught SecurityError: Failed to execute 'open' on 'IDBFactory':
          //                              access to the Indexed Database API is denied in this context.
          var open = indexedDB.open("MyDatabase", 1);

          open.onsuccess = function()
          {
              // Start a new transaction
              var db = open.result;
              var tx = db.transaction("MyObjectStore", "readwrite");
              var store = tx.objectStore("MyObjectStore");
              var index = store.index("NameIndex");

              // Add some data
              store.put({id: 12345, name: {first: "John", last: "Doe"}, age: 42});
              store.put({id: 67890, name: {first: "Bob", last: "Smith"}, age: 35});

              // Close the db when the transaction is done
              tx.oncomplete = function()
              {
                  db.close();
              };
          }
        }//end job()

        function notRecognized(orden)
        {
            var mensaje = 'Comando no reconocido';
            selt.postMessage(mensaje + ': ' + orden);
        }
  </script>






    <script type="text/javascript">

        var myWorker;
        var workerStarted = false;

        //Al cargar la pagina, se llama al onload, que carga el WebWorker
        window.onload = function () {

            var blob = new Blob([ document.querySelector('#worker').textContent ], {type : 'text/javascript'});

            myWorker = new Worker(window.URL.createObjectURL(blob));

            myWorker.onmessage = function (event)
            {
                document.getElementById("demo").textContent = event.data; //cambiamos el texto del <p>
                console.log("Got: " + event.data + "\n");
            };

            myWorker.onerror = function (error)
            {
                document.getElementById("demo").textContent = "Worker error: " + error.message;
                console.log("Worker error: " + error.message + "\n");
                throw error;
            };
        };//e onload

      //click en botón iniciar, mandamos 'start' al worker
      function startWorker()
      {
         if(workerStarted)
         {
            document.getElementById("demo").textContent = "Worker yet started !";
            return;
          }


          //Create the DataBase
          var indexedDB = window.indexedDB || window.mozIndexedDB || window.webkitIndexedDB || window.msIndexedDB || window.shimIndexedDB;

          // Open (or create) the database
          var open = indexedDB.open("MyDatabase", 1);

          // Create the schema
          open.onupgradeneeded = function() {
              var db = open.result;
              var store = db.createObjectStore("MyObjectStore", {keyPath: "id"});
              var index = store.createIndex("NameIndex", ["name.last", "name.first"]);
          };

          workerStarted = true;

          //Start Worker
          myWorker.postMessage('start');
      }

      //click en botón parar, mandamos 'stop' al worker
      function stopWorker() {
          myWorker.postMessage('stop');
      }
    </script>
  </body>

  </html>