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Detailed explanation of the height of the browser scroll bar in js

零下一度Original: 2017-07-09 10:25:361562browse

The following editor will bring you an article about the height scrolltop of the js browser scroll bar (Example explanation). The editor thinks it’s pretty good, so I’ll share it with you now and give it as a reference. Let’s follow the editor and take a look.

1. In the JSbox model we learned before: client series/offset series/scrollWidth/scrollHeight are all “read-only” attributes-> ; The value can only be obtained through attributes, and the style of the element cannot be modified through attributes.

2. scrollTop/scrollLeft: the height/width of the scroll bar (these two attributes are the only "readable and writable" attributes)

box.scrollTop = 0 // Return directly to the top of the container

The value of our scrollTop has boundary values (maximum and minimum values), and the value we set is smaller than the minimum value or It is useless if it is larger than the maximum value. The effect is still the boundary value

[The minimum value is zero]

box.scrollTop = -1000;// Returns directly to the top of the container, without exceeding

console.log(box.scrollTop) //0

[Maximum value = true height -The height of the current container one screen]

var maxTop = box.scrollHeight - box.clientHeight;

The most classic application of scrollTop is to return to the top. The following code is as follows ：

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    *{
      padding:0;
      margin:0;
    }
    html,body{
      width:100%;
      height:1000%;
      background:#11c900;
    }
    a{
      text-decoration: none;
      color:#000;

    }
  </style>
</head>
<body>
<a href="javascript:" rel="external nofollow" id="goLink">GO</a>
//A标签本身是跳转页面的，把跳转的地址写在href这个属性中
/*
  1）、不写值的话是刷新本页面
  2）、写的如果是#target，是锚点定位，定位到当前页面Id为target这个位置
  3）、“javascript:”这样写是取消A标签默认跳转的行为
*/
<script>
  var goLink =document.getElementById("goLink");
  /*
    回到顶部：
    总时间（duration）:500ms 
    频率（interval）：多长时间走一步 10ms 
    总距离(target): 当前的位置（当前的scrollTop）- 目标的位置(0)
    步长(step)：每一次走得距离  (target/duration)*interval 
  */


  /*
    这个代码是可以优化的:
    开始GO按钮是不显示的，当滚动到一定的距离之后，才显示，反之隐藏 只要浏览器的滚动条在滚动，我们就需要判断GO显示还是隐藏
    浏览器的滚动条滚动:拖动滚动条、鼠标滚轮、键盘上下键、pageDown/pageUp键、点击滚动条的空白区域或者箭头（自主操作的行为）...我们还可以通过js控制scrollTop的值来实现滚动条的滚动
  */

  window.onscroll = function computedDisplay(){//不管怎么操作的，只要滚动条动了就会触发这个行为
    var curTop = document.documentElement.scrollTop || document.body.scrollTop;
    var curHeight = document.documentElement.clientHeight || document.body.clientHeight;
    if(curTop>=clientHeight){
      goLink.style.display = "block"
    }else{
      goLink.style.display = "none"
    }

  }
  goLink.onclick = function(){
    this.style.display = "none";//并不会消失，因为我们滚动条往回走的时候 又会触发onscroll事件，又会进行显示
    window.onscroll = null;
    var duration = 500,interval=10,target=document.documentElement.scrollTop || document.body.scrollTop;
    var step = (target/duration)*interval;

    var timer = window.setInterval(function(){
      var curTop = document.documentElement.scrollTop || document.body.scrollTop;
      if(curTop===0){
        window.clearInterval(timer);
        window.onscroll = computedDisplay;
        //当动画结束后把对应的方法重新绑定给window.onscroll
        return;
      }
      curTop-=step
      document.documentElement.scrollTop = curTop;
      document.body.scrollTop = curTop;
    },interval)
    // document.documentElement.scrollTop = 0;
    // document.body.scrollTop = 0;
  }
</script>
</body>
</html>

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