code: function getId(element) {
          var state = getState(element);
  
          if (state && state.id !== undefined) {
              return state.id;
          }
  
          return null;
      }
docs: Gets the resize detector id of the element.
  @public
  @param {element} element The target element to get the id of.
  @returns {string|number|null} The id of the element. Null if it has no id.