<script type="text/javascript">
function check_box() {
var count=document.myform.checkThis.length;
//var count=document.getElementById('checkThis').length;
alert(count);
var j=0;
for(var i=0;i<count;i++)
{
if (document.myform.checkThis[i].checked)
//if (document.myform.checkThis[i].checked)
//document.getElementById('checkThis').checked;
++j;
}
if(j==0) {
alert("至少选择一个!!");
return false;
}
else
{
return true;
}
}
</script>
<form name="myform" action="" onsubmit="return check_box();">
<input type="checkbox" name="checkThis" value="1">1<br>
<input type="checkbox" name="checkThis" value="2">2<br>
<input type="checkbox" name="checkThis" value="3">3<br>
<input type="submit" value="提交" >
</form>