[javascript] Confirm postback OnClientClick button ASP.NET

<asp:Button runat="server" ID="btnUserDelete" Text="Delete" CssClass="GreenLightButton"
                           OnClick="BtnUserDelete_Click"
                           OnClientClick="return UserDeleteConfirmation();" 
 meta:resourcekey="BtnUserDeleteResource1" />

I have tried:

function UserDeleteConfirmation() {
        if (confirm("Are you sure you want to delete this user?"))
            return true;
        else
            return false;
}

and

function UserDeleteConfirmation() {
    if (confirm("Are you sure you want to delete this user?")) {
            __doPostBack(btnUserDelete, '');
    }

    return false;
 }

And none of them works.

I know this is old and there are so many answers, some are really convoluted, can be quick and inline:

<asp:Button runat="server" ID="btnUserDelete" Text="Delete" CssClass="GreenLightButton" OnClick="BtnUserDelete_Click" OnClientClick="return confirm('Are you sure you want to delete this user?');" meta:resourcekey="BtnUserDeleteResource1" />
                       

This is a simple way to do client-side validation BEFORE the confirmation. It makes use of the built in ASP.NET validation javascript.

<script type="text/javascript">
    function validateAndConfirm() {
        Page_ClientValidate("GroupName");  //'GroupName' is the ValidationGroup
        if (Page_IsValid) {
            return confirm("Are you sure?");
        }
        return false;
    }
</script>

<asp:TextBox ID="IntegerTextBox" runat="server" Width="100px" MaxLength="6" />
<asp:RequiredFieldValidator ID="reqIntegerTextBox" runat="server" ErrorMessage="Required"
    ValidationGroup="GroupName"  ControlToValidate="IntegerTextBox" />
<asp:RangeValidator ID="rangeTextBox" runat="server" ErrorMessage="Invalid"
    ValidationGroup="GroupName" Type="Integer" ControlToValidate="IntegerTextBox" />
<asp:Button ID="SubmitButton" runat="server" Text="Submit"  ValidationGroup="GroupName"
    OnClick="SubmitButton_OnClick" OnClientClick="return validateAndConfirm();" />

Source: Client Side Validation using ASP.Net Validator Controls from Javascript

try this :

<asp:Button runat="server" ID="btnUserDelete" Text="Delete" CssClass="GreenLightButton" 
   onClientClick=" return confirm('Are you sure you want to delete this user?')" 
   OnClick="BtnUserDelete_Click"  meta:resourcekey="BtnUserDeleteResource1"  />

try this : OnClientClick="return confirm('Are you sure ?');" Also set : CausesValidation="False"

Try this:

function Confirm() {
    var confirm_value = document.createElement("INPUT");
    confirm_value.type = "hidden";
    confirm_value.name = "confirm_value";

        if (confirm("Your asking")) {
            confirm_value.value = "Yes";
            document.forms[0].appendChild(confirm_value);
        }
    else {
        confirm_value.value = "No";
        document.forms[0].appendChild(confirm_value);
    }
}

In Button call function:

<asp:Button ID="btnReprocessar" runat="server" Text="Reprocessar" Height="20px" OnClick="btnReprocessar_Click" OnClientClick="Confirm()"/>

In class .cs call method:

        protected void btnReprocessar_Click(object sender, EventArgs e)
    {
        string confirmValue = Request.Form["confirm_value"];
        if (confirmValue == "Yes")
        {

        }
    }

The code is like this:

In Aspx:

<asp:Button ID="btnSave" runat="server" Text="Save" OnClick="btnSave_Click" CausesValidation=true />

in Cs:

protected void Page_Load(object sender, System.EventArgs e)
{
     if (!IsPostBack)
     {
         btnSave.Attributes["Onclick"] = "return confirm('Do you really want to save?')";          
     }
}

protected void btnSave_Click(object sender, EventArgs e){
    Page.Validate();
    if (Page.IsValid)
    {
       //Update the database
         lblMessage.Text = "Saved Successfully";
    }
}

Using jQuery UI dialog:

SCRIPT:

<link rel="stylesheet" href="http://code.jquery.com/ui/1.9.2/themes/base/jquery-ui.css" />
<script src="http://code.jquery.com/jquery-1.8.3.js"></script>
<script src="http://code.jquery.com/ui/1.9.2/jquery-ui.js"></script>
<script>
 $(function () {

            $("#<%=btnUserDelete.ClientID%>").on("click", function (event) {
                event.preventDefault();
                $("#dialog-confirm").dialog({
                    resizable: false,
                    height: 140,
                    modal: true,
                    buttons: {
                        Ok: function () {
                            $(this).dialog("close");
                            __doPostBack($('#<%= btnUserDelete.ClientID %>').attr('name'), '');
                        },
                        Cancel: function () {
                            $(this).dialog("close");
                        }
                    }
                });
            });
 });
</script>

HTML:

<div id="dialog-confirm" style="display: none;" title="Confirm Delete">
    <p><span class="ui-icon ui-icon-alert" style="float: left; margin: 0 7px 20px 0;"></span>Are you sure you want to delete this user?</p>
</div>

You can put the above answers into one line like this. And you don't need to write the function.

    <asp:Button runat="server" ID="btnUserDelete" Text="Delete" CssClass="GreenLightButton"
         OnClick="BtnUserDelete_Click" meta:resourcekey="BtnUserDeleteResource1"
OnClientClick="if ( !confirm('Are you sure you want to delete this user?')) return false;"  />

Try this:

<asp:Button runat="server" ID="btnDelete" Text="Delete"
   onClientClick="javascript:return confirm('Are you sure you want to delete this user?');" OnClick="BtnDelete_Click" />

There are solutions here that will work, but I don't see anyone explaining what is actually happening here, so even though this is 2 years old I'll explain it.

There is nothing "wrong" with the onclientclick javascript you are adding. The problem is that asp.net is adding it's on onclick stuff to run AFTER whatever code you put in there runs.

So for example this ASPX:

<asp:Button ID="btnDeny" runat="server" CommandName="Deny" Text="Mark 'Denied'" OnClientClick="return confirm('Are you sure?');" />

is turned into this HTML when rendered:

<input name="rgApplicants$ctl00$ctl02$ctl00$btnDeny" id="rgApplicants_ctl00_ctl02_ctl00_btnDeny" 
onclick="return confirm('Are you sure?');__doPostBack('rgApplicants$ctl00$ctl02$ctl00$btnDeny','')" type="button" value="Mark 'Denied'" abp="547">

If you look closely, the __doPostBack stuff will never be reached, because the "confirm" will always return true/false before __doPostBack is reached.

This is why you need to have the confirm only return false and not return when the value is true. Technically, it doesn't matter if it returns true or false, any return in this instance would have the effect of preventing the __doPostBack from being called, but for convention I would leave it so that it returns false when false and does nothing for true.