盒子的偏移量

盒子相对于offsetParent偏移量:offsetLeft,offsetTop.
offsetParent:盒子向上找的第一个有定位的元素,没有就是body,body的offsetParent是null
现在,想求任意盒子相对body的偏移量.<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>
  * {
    padding: 0;
    margin: 0;
    font-size: 14px;
  }
   #outer {
     300px;
    height: 300px;
    padding: 50px;
    margin: 30px;
    border: 10px solid #000;
    background-color: pink;
  }
  
  #inner {
     200px;
    height: 200px;
    padding: 40px;
    margin: 30px;
    border: 10px solid #000;
    background-color: #69f;
  }
  
  #center {
     100px;
    height: 100px;
    padding: 30px;
    margin: 30px;
    border: 10px solid #000;
    background-color: #6f9;
  }
  </style>
</head>

<body>
  <div id="outer">
    <div id="inner">
      <div id="center"></div>
    </div>
  </div>
  <script>
  var outer = document.getElementById("outer");
  var inner = document.getElementById("inner");
  var center = document.getElementById("center");
  console.log(center.offsetParent); // body
  console.log(center.offsetLeft); // 200,这里是center这个盒子(包括border)的左上角离inner盒子内容区(不包括border)的左上角的距离
  console.log(center.offsetTop); // 200
  inner.style.position = outer.style.position = "relative";
  console.log(center.offsetParent); // inner
  console.log(center.offsetLeft); // 70,这里是center这个盒子(包括border)的左上角离inner盒子内容区(不包括border)的左上角的距离
  console.log(center.offsetTop); // 70
  console.log(inner.offsetParent); // outer
  console.log(inner.offsetLeft); // 80
  console.log(inner.offsetTop); // 80
  console.log(outer.offsetParent); // body
  console.log(outer.offsetLeft); // 30
  console.log(outer.offsetTop); // 30
  // center相对body的偏移量
　console.log(center.offsetLeft + (center.offsetParent.clientLeft + center.offsetParent.offsetLeft) + (center.offsetParent.offsetParent.clientLeft + center.offsetParent.offsetParent.offsetLeft)); // 200
  function offset(ele) {
    var
      parent = ele.offsetParent,
      left = ele.offsetLeft,
      top = ele.offsetTop;
　　// 只要不是null
    while (parent) {
      // ie8的offset已经加上了父元素的clientLeft
      if (navigator.userAgent.indexOf("MSIE 8.0") === -1) {
        // 父级参照物的边框
        left += parent.clientLeft;
        top += parent.clientTop;
      }
      left += parent.offsetLeft;
      top += parent.offsetTop;
      parent = parent.offsetParent;
    }
    return {
      left,
      top
    };
  }
  console.log(offset(center))
  </script>
</body>

</html>