复选框全选、反选效果

<script language="javascript">
function selectAll(obj){
    for(var i=0; i<obj.elements.length; i++)
    if(obj.elements[i].type == "checkbox")
        obj.elements[i].checked = true;
}

function invert(obj){
    for(var i=0; i<obj.elements.length; i++)
    if(obj.elements[i].type == "checkbox" )
        obj.elements[i].checked = !obj.elements[i].checked;
}
</script>
<form name="products_listing">
<input type="checkbox" name="products[]" value="1">1
<input type="checkbox" name="products[]" value="2">2
<input type="checkbox" name="products[]" value="3">3
<input type="checkbox" name="products[]" value="4">4
<input type="checkbox" name="products[]" value="5">5
<input type="checkbox" name="products[]" value="6">6
<input type="button" value="Select All" onclick="selectAll(document.products_listing)">
<input type="button" value="Invert" onclick="invert(document.products_listing)">
</form>