遍历 DOM 节点去动态计算最大 zIndex.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .pop1{ position: relative; z-index: 1;}
    .pop2{ position: relative; z-index: 2;}
    .pop3{ position: relative; z-index: 4;}
    .pop4{ position: relative; z-index: 89;}
    .pop5{ position: relative; z-index: 10;}
  </style>
</head>
<body>
  <div class="pop1"></div>  
  <div class="pop2"></div>  
  <div class="pop3"><div class="pop4"></div></div> 
  <div class="pop5"><div class="pop6"></div><div class="pop7"></div></div>  
</body>
<script>
  function getZIndex(){
      return [...document.all].reduce((r, e) => Math.max(r, +window.getComputedStyle(e).zIndex || 0), 0)
  }
  console.log('getZIndex',getZIndex())
</script>
</html>