code: function memorizeHandler(element, type, keyFn, valueFn) {
      const map = safeEvent(element, type);
      let items = map.get(keyFn);
  
      if (items) {
          items.push(valueFn);
      } else {
          items = [valueFn];
          map.set(keyFn, items);
      }
  }
docs: Memorize DOM event handler for unbinding
  @param {HTMLElement} element - element to bind events
  @param {string} type - events name
  @param {function} keyFn - handler function that user passed at on() use
  @param {function} valueFn - handler function that wrapped by domevent for
  implementing some features