JavaScript 获取 DOM 元素 class 的两种实现方式

<!DOCTYPE html>
<html>
<head lang="en">
 <meta charset="UTF-8">
 <title></title>
 <script>
  function getClass(node,classname) { 
   if(node.getElementsByClassName) {
    return node.getElementsByClassName(classname);
 //如果存在该标签 就返回
   } else {
    var elems = node.getElementsByTagName(node),
      defualt = [];
    for (var i = 0; i < elems.length; i++) {
 //遍历所有标签
     if(elems[i].className.indexOf(classname) != -1) {
 //查找相应类名的标签
      defualt[defualt.length] = elems[i];
     }
    }
    return defualt;
   }
  }
   window.onload = function () {
   var text = document.getElementById('text'),
    cs = getClass(text,'cs');
     document.write(cs.innerHTML='cs');
  }
 </script>
</head>
<body>
 <div id="text"><div class="cs">textcss</div></div>
</body>
</html>