checkbox全选与不全选的切换

    <input type=checkbox name=mm value=a onclick="checkItem(this, 'mmAll')"><br>
<input type=checkbox name=mm value=b onclick="checkItem(this, 'mmAll')"><br>
<input type=checkbox name=mm value=c onclick="checkItem(this, 'mmAll')"><br>
<input type=checkbox name=mm value=d onclick="checkItem(this, 'mmAll')"><br>
<input type=checkbox name=mm value=e onclick="checkItem(this, 'mmAll')"><br><br>

<input type=checkbox name=mmAll onclick="checkAll(this, 'mm')">全选与不全选的切换

<script language=Javascript>
    function checkAll(e, itemName) {
        var aa = document.getElementsByName(itemName);
        for (var i = 0; i < aa.length; i++)
            aa[i].checked = e.checked;
    }
    function checkItem(e, allName) {
        var all = document.getElementsByName(allName)[0];
        if (!e.checked) all.checked = false;
        else {
            var aa = document.getElementsByName(e.name);
            for (var i = 0; i < aa.length; i++)
                if (!aa[i].checked) return;
            all.checked = true;
        }
    }
</script>