window.onload = function () {

  //获取鼠标滑过或点击的标签和要切换内容的元素

  var titles = $('notice-tit').getElementsByTagName('li');

  var divs = $('notice-con').querySelectorAll('div');

  alert(titles.length)

}

bug这是啥意思？

script.js:9 Uncaught TypeError: Cannot read property 'querySelectorAll' of null

    at window.onload (script.js:9)