You can write a function in the JS for comparison as follows
1.
function fnCheck()
{
if(!confirm(‘Are you quite sure?’)) return false;
}
on ClientClick of your button write following code
<asp:Button ID="btnSave" runat="server" Text="Save" OnClick="lnkbtnSave_Click" OnClientClick="javascript: return fnCheck();">
in this case it JS returns false, it does not go to server for execution.
2.
Or you can add an attribute to that button to execute JS.
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