全选，不选，反选js

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="author" content="" />
<meta name="copyright" content="" />
<title></title>
<style>
*{ margin:0; padding:0; list-style:none; font-family: "微软雅黑","张海山锐线体简"}
#div1{border-top:#333 10px solid;}
</style>
<script>
window.onload=function(){
    var oBtn=document.getElementById('btn1');
    var oBtn2=document.getElementById('btn2');
    var oBtn3=document.getElementById('btn3');
    var oDiv=document.getElementById('div1');
    var aIpt=oDiv.getElementsByTagName('input');
    //全选
    oBtn.onclick=function(){
        for(var i=0;i<aIpt.length;i++){
            aIpt[i].checked=true;
        }
    };
    //不选
    oBtn2.onclick=function(){
        for(var i=0;i<aIpt.length;i++){
            aIpt[i].checked=false;
        }
    };

    //反选
    oBtn3.onclick=function(){
        for(var i=0;i<aIpt.length;i++){
            aIpt[i].checked=!aIpt[i].checked;
        }
    };
};
</script>
</head>

<body>

<input type="button" value="全选" id="btn1">
<input type="button" value="不选" id="btn2">
<input type="button" value="反选" id="btn3">

<div id="div1">
    <input type="checkbox" checked="true"><br>
    <input type="checkbox"><br>
    <input type="checkbox"><br>
    <input type="checkbox"><br>
    <input type="checkbox"><br>
</div>

</body>
</html>