淡入功能无效

Question

I am very new to jQuery, so please bear with me. I'm trying to make a div whose class is called "cover" fade in using its opacity CSS attribute. Here's the jQuery:

var div = $('.cover');
var divH = div.height();
$(window).on('scroll', function() {
  var st = $(this).scrollTop();
  div.css({ 'opacity' : (0 + st/divH) });
});

I have a JSFiddle with the CSS and HTML bits here: http://jsfiddle.net/ShubhangD/6xm0o8ta/ . This seems like a simple thing to do, but it's not working at all. Can anyone please help me out?

Thanks in advance! :)

Answer 1

您在代码中缺少此脚本标记：

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>‌​