当DOM到达DOM元素的末尾时触发函数

Question

当我们继续滚动时，我们会在特定时间到达divOne的末尾。那时我希望divTwo为relative（最初是fixed）。这是我的代码。请帮忙

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.divOne {
  height: 800px;
  width: 100%;
  background-color: #000;
}

.divTwo {
  height: 50px;
  width: 100%;
  position: fixed;
  bottom: 0;
  background-color: brown;
}

.divThree {
  height: 100px;
  width: 100%;
  background-color: pink;
}

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<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<div class="divOne"></div>
<div class="divTwo"></div>
<div class="divThree"></div>

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