JavaScript实现复选框全选与取消全选功能详解

<html>
<head>
 <meta charset=" utf-8">
 <meta name="author" content="http://hovertree.com/" />
 <title>JS实现复选框的全选和取消全选 - 何问起</title><base target="_blank" />
 <style type="text/css">
  li {
   list-style-type: none;
   font-size: 12px;
   color: blue;
   width: 300px;
   height: 20px;
   line-height: 20px;
  }
  a {
   width: 200px;
   height: 20px;
   float: left;
  }
  .ck {
   float: left;
   width: 26px;
  }
  .time {
   color: red;
   width: 60px;
   height: 20px;
   float: right;
  }
  .dohovertree {
   font-size: 12px;
  }
 </style>
 <script type="text/javascript">
window.onload=function()
{
 var checkboxs=document.getElementsByName("myHove"+"rTreechk");
 var hvtck=document.getElementById("hvtck");
 cklen=checkboxs.length;
 hvtck.onclick=function()
 {
 if(this.checked==true)
 {
  for(var i=0;i<cklen;i++)
  {
  checkboxs[i].checked=true;
  }
  document.getElementById("dohovert"+"ree").innerHTML="取消"
 }
 else
 {
  for(var i=0;i<cklen;i++)
  {
  checkboxs[i].checked=false;
  }
  document.getElementById("dohovertree").innerHTML="全选"
 }
 }
}
 </script>
</head>
<body>
 <h3>JS实现复选框的全选和取消全选 何问起</h3>
 <div style="width:736px">
  <a href="http://hovertree.com">首页</a> <a href="http://hovertree.com/texiao/">更多特效</a> <a href="http://hovertree.com/hvtart/bjae/91eqf5ge.htm">原文</a>
 </div>
 <div>
  <ul>
   <li>
    <span class="ck"><input type="checkbox" name="myHoverTreechk" /></span>
    <a href="http://hovertree.com/">何问起欢迎您</a>
    <span class="time">2014-12-13</span>
   </li>
   <li>
    <span class="ck"><input type="checkbox" name="myHoverTreechk" /></span>
    <a href="http://hovertree.com/hvtart/bjae/91eqf5ge.htm">大家好，好久不见了</a>
    <span class="time">2015-12-03</span>
   </li>
   <li>
    <span class="ck"><input type="checkbox" name="myHoverTreechk" /></span>
    <a href="http://hovertree.com/menu/javascript/">何问起JS</a>
    <span class="time">2015-11-13</span>
   </li>
  </ul>
  <div>
   <input type="checkbox" id="hvtck" />
   <span class="dohovertree" id="dohovertree">全选</span>
  </div>
 </div>
</body>
</html>

var checkboxs=document.getElementsByName("myHove"+"rTreechk");
var hvtck=document.getElementById("hvtck");