jquery 阻止表单提交方法

<form name="message_form" action="?m=mobilecenter&c=index&a=service" method="post" onsubmit="javascript:chkservice(this);return false;">

</form>

function chkservice(From){
    var tags = false;
    if(tags){
        alert('禁止提交');
        return false;
    }
    From.submit();
    return true;
}