采用dom实现复选框全选、取消效果

<form action="">
爱好：<br/>
<input type="checkbox" id="all">全选<br/>
<input type="checkbox"  name="hobby" value="唱歌">唱歌
<input type="checkbox"  name="hobby" value="跳舞">跳舞
<input type="checkbox"  name="hobby" value="学习">学习
<input type="checkbox"  name="hobby" value="玩耍">玩耍<br/>
<button id="choice" value="选择">选择</button>
</form>

<script>
window.onload = function(){
document.getElementById("all").addEventListener("click",function(){
var a = document.getElementById("all");
var b = document.getElementsByName("hobby");
for(var i=0;i< b.length;i++) {
b[i].checked = a.checked;
}
},false)
}

</script>