code: function _generateHandler(element, waitingOn, callback) {
      return function _handleResponseFromWorker(data) {
          element.innerHTML = data.result;
          element.classList.remove('loading');
          element.classList.add('rainbow-show');
  
          if (element.parentNode.tagName === 'PRE') {
              element.parentNode.classList.remove('loading');
              element.parentNode.classList.add('rainbow-show');
          }
  
          // element.addEventListener('animationend', (e) => {
          //     if (e.animationName === 'fade-in') {
          //         setTimeout(() => {
          //             element.classList.remove('decrease-delay');
          //         }, 1000);
          //     }
          // });
  
          if (onHighlightCallback) {
              onHighlightCallback(element, data.lang);
          }
  
          if (--waitingOn.c === 0) {
              callback();
          }
      };
  }
docs: Browser Only - Handles response from web worker, updates DOM with
  resulting code, and fires callback
  
  @param {Element} element
  @param {object} waitingOn
  @param {Function} callback
  @return {void}