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Detailed explanation of js to determine whether the content area is scrolled to the bottom

小云云Original: 2017-12-21 09:35:092854browse

To determine whether the content is scrolled to the end, you need to know the real height of the content area (that is, the scroll area), the position of the scroll bar from the top, and the visible height of the content area. This article mainly shares a js native judgment of whether the content area has scrolled to the bottom. The example code has a good reference value. I hope it can help everyone.

corresponds to the following three APIs respectively.

element.scrollHeight Gets the content height of the element,,, [Read-only attribute]

element.scrollTop can get or set the offset value of the element. It is often used to calculate the position of the scroll bar. If the container of an element does not generate a vertical scroll bar, its scrollTop value defaults to 0.

element.clientHeight Reads the visible height of the element [read-only attribute]

Directly below Quoting a classic formula on MDN

Determine whether the element scrolls to the end

If the element scrolls to the end, the following equation returns true, otherwise it returns false.

element.scrollHeight - element.scrollTop === element.clientHeight

Case-User Agreement

Only after the user has finished reading the agreement can they click to agree, which means that after the scroll bar reaches the bottom, it means Finish reading

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>tab</title>
  <style>
    textarea{height: 200px;width: 300px}
  </style>
</head>
<body>

<p>
  <textarea>
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  </textarea>
</p>
<p>
  <input type="checkbox" value="1" disabled="disabled"> 同意
</p>
<script>
  //获取checkbox元素
  var checkbox=document.querySelector(&#39;input[type=checkbox]&#39;);

  document.querySelector(&#39;textarea&#39;).addEventListener(&#39;scroll&#39;,function () {

    //读取内容区域的真实高度（滚动条高）
//    console.log(this.scrollHeight);

    //读取滚动条的位置
//    console.log(this.scrollTop);

    //设置滚动到的位置
//      this.scrollTop=800;

    //读取元素的高度
//    console.log(this.clientHeight)

    //意思就是内容总体的高度 - 滚动条的偏移值 === 元素的高度(包含内边)但不包含外边距，边框，以及滚动条
    if(this.scrollHeight-this.scrollTop===this.clientHeight){
      console.log("到达底部");
      //移除disabled属性
      checkbox.removeAttribute(&#39;disabled&#39;)
    }

  })


</script>
</body>
</html>

Okay, today I suddenly saw this API on mdn. I thought about it
Element.scrollTop

Have you learned it? Hurry up and give it a try.

Related recommendations:

Implementation of the div internal scroll bar scrolling to the bottom and top functions

jquery page scrolling to the bottom Automatically load plug-in collection_jquery

Javascript implements code for DIV scrolling to automatically scroll to the bottom_javascript skills

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