function check() {
var str = $("input[id$=Tbpassword]").val();//文本框解析之后为input,找到id以Tbpassword结尾的,
if (str=="") {
alert("密码不能为空");
$("*id[$=Tbpassword]").focus();
return false;
} else {
return true;
}
}
<asp:LinkButton ID="DelControlArea" runat="server" CausesValidation="False" Text="删除" OnClientClick="return check()" OnClick="DelControlArea_OnClick"></asp:LinkButton>