How to use confirm function of java script

Your html code is as follows.

<asp:Button ID="btnCancel" CssClass="Btn" runat="server"

                                                                        Text="Cancel" OnClick="btnCancel_Click" />

Your Javascript code:

function AskConfirm()

          {

            var answer;

            answer = confirm("Are you sure you want to submit this Booking?");

            if (answer == false)

            {    

                return false;      

            }

            return true;

          }

Your pagebehind code:

protected void Page_Load(object sender, EventArgs e)

    {

        btnCancel.Attributes.Add("onclick", "javascript:return AskConfirm();");

}

protected void btnCancel_Click(object sender, EventArgs e)

    {

        Response.Redirect("OnlineReservation.aspx");

    }

Instead of calling the javascript function in html button code I have called it from pagebehind. You can use any one of the method.

Now as soon as you hit the cancel button it will ask for confirmation if you say no it will go to javascript code first and will found the if loop condition where we check answer == false and inside the loop as we mentioned return false,it will stop execution and it will not execute any further code. But in case of answer = true it will not go inside the loop and it will find return true at the end of function,which allows to go to server side assosiated with the cancel button in server side and execute it.