判斷滾軸區塊.js

(function($) {
  var dataLayer =  window.dataLayer || [];
  var eventString = 'cusevent';
  var eventCategoryString = '張曼娟活動頁';
  
  var areaIndex = 0;
  var areaIndexArr = [];

  $(window).scroll(function() {
    var windowHeight = $(window).height();
    var scrollPosition;
    $('header, .area2, .area3').each(function (i) {
      var $this = $(this);
      var thisTop = $this.offset().top;
      var winHalfHeight = windowHeight / 2;
      var scrollTop = $(window).scrollTop();
      scrollPosition = scrollTop + windowHeight;

      // 滑到超過螢幕的一半
      if (scrollPosition >= thisTop + winHalfHeight) {
        areaIndex = i;
      }
    });

    // 還沒有滑到過的區域
    if (areaIndexArr.indexOf(areaIndex) === -1) {
      areaIndexArr.push(areaIndex);
      var areaName = '';
      switch(areaIndex) {
        case 0:
          areaName = '1.文學繪本';
          break;
        case 1:
          areaName = '2.歷年著作';
          break;
        case 2:
          areaName = '3.文學學堂';
          break;
        default:
          areaName = '';
      }
      pushDatalayer('滾軸事件', areaName);
    }
  }).scroll();
  
  function pushDatalayer(thisAction, thisLabel) {
    dataLayer.push({
      event: eventString,
      eventCategory: eventCategoryString,
      eventAction: thisAction,
      eventLabel: thisLabel
    });
  }
})(jQuery)