验证用户必选CheckBox控件与自定义验证javascript代码

function ValidateCheckBox(sender, args) {
var checkbox = document.getElementById("<%=CheckBox1.ClientID %>")
if (checkbox.checked) {
args.IsValid = true;
}
else {
args.IsValid = false;
}
}

<asp:CheckBox ID="CheckBox1" runat="server" />
<asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="必须选择选项" ForeColor="Red" ClientValidationFunction="ValidateCheckBox"></asp:CustomValidator><br />
<asp:Button ID="Button1" runat="server" Text="提交" />