function btnSelete_Click() {
var strconfirm = confirm("Are you sure you want to delete?");
if (strconfirm == true) {
return true;
}
}
<asp:Button ID="btnSelect" runat="server" Text="Select" Onclientclick="return btnSelete_Click();" CssClass="cssbutton" />
How to create a yes/no/cancel alert box instead of ok/cancel alert box in Javascript?
You can use jQuery UI Dialog.
These libraries create HTML elements that look and behave like a dialog box, allowing you to put anything you want (including form elements or video) in the dialog.