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.

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

    <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 type="button" onclick="stopWorker()" id="btnStop">
        Stop WebWorker

  <p id="demo"></p>

  <script src=""></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 =;

            switch (orden)
                case 'start':
                case 'stop':

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

        function stop()
                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 ="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()
        }//end job()

        function notRecognized(orden)
            var mensaje = 'Comando no reconocido';
            selt.postMessage(mensaje + ': ' + orden);

    <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 =; //cambiamos el texto del <p>
                console.log("Got: " + + "\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()
            document.getElementById("demo").textContent = "Worker yet started !";

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

          // Open (or create) the database
          var 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

      //click en botón parar, mandamos 'stop' al worker
      function stopWorker() {




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