JS实现全选

<script language="javaScript">    

//全选或全部不选    
function checkall() {    
    var isChecked=(document.form1.checkAll.checked == true);    
    var elements_all=document.form1.elements;    
    for(i=0;i<elements_all.length;i++) {    
        var element=elements_all[i];    
        if(element.type=="checkbox")  {    
            element.checked=isChecked;    
        }    
    }    
}    

//是否有checkbox被选中    
function anyChecked() {    
    var elements_any=document.form1.elements;    
    for(i=0;i<elements_any.length;i++) {    
        var element=elements_any[i];    
        if(element.checked == true) {    
            return true;    
        }    
    }    
    return false;    
}    

</script>

<form name="form1" Method="post" action="" onsubmit="return anyChecked()">    
全选:<input type="checkbox" id="checkAll"onclick="checkall()" />    
多项选择框列表:    
<input type="checkbox" name="cb" value="1"/>    
<input type="checkbox" name="cb" value="2"/>    
<input type="checkbox" name="cb" value="3"/>    
<input name="Submit" type="submit" value="submit">    
</form>