code: function () {
  
          if(this.data.debug){
              console.log('Initialized preloader');
          }
  
          if(this.data.type === 'bootstrap' && typeof $ === 'undefined'){
              console.error('jQuery is not present, cannot instantiate Bootstrap modal for preloader!');
          }
  
          document.querySelector('a-assets').addEventListener('loaded',function(){
              if(this.data.debug){
                  console.info('All assets loaded');
              }
              this.triggerProgressComplete();
  
          }.bind(this));
  
          var assetItems = document.querySelectorAll('a-assets a-asset-item,a-assets img,a-assets audio,a-assets video');
  
          this.totalAssetCount = assetItems.length;
  
          this.watchPreloadProgress(assetItems);
  
          if(!this.data.target && this.data.autoInject){
              if(this.data.debug){
                  console.info('No preloader html found, auto-injecting');
              }
              this.injectHTML();
          }else{
              switch(this.data.type){
                  case 'bootstrap':
                      this.initBootstrapModal($(this.data.target));
                      break;
                  default:
                      //do nothing
                      break;
              }
          }
  
          if(this.data.disableVRModeUI){
              this.sceneEl.setAttribute('vr-mode-ui','enabled','false');
          }
      }
docs: length of time to slow down preload finish if slowLoad is set to 'true' 
  Called once when component is attached. Generally for initial setup.