code: function createWorker() {
      var worker = new Worker('worker.js');
  
      // On worker messsage
      worker.onmessage = function(event) {
          if (event.data.event === 'done') {
              console.log('done:', event.data.data);
              $('#start').show();
              $('#abort').hide();
          }
          else if (event.data.event === 'progress') {
              console.log('progress:', event.data.data.percent, '%');
          }
      };
  
      return worker;
  }
docs: Create and return the Worker object