How to apply javascript on asp.net button click?

I hope this can be of some help. I must confess that what you want to achieve is not clear to me.

<script type="text/javascript">
     myClosure=function() {
        var canyousee = "here I'm ";
        return (function () {
            return { canyouseeIt: function(){return confirm (canyousee)}};
        });
    }
</script>


<asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="(myClosure())().canyouseeIt()" />

function msg() {
    window.setTimeout(function () {
        $(".alert").fadeTo(1500, 0).slideUp(500, function () {
            $(this).remove();
        });
    }, 5000);
}

You're declaring your function inside your ready. Declare it outside of it.

$(document).ready(...); basically says "when my document is finished rendering, run the code within." You don't want to do that, you just want to declare your function for use in your OnClientClick. If you move msg() out of the .ready(), it should work.

Also, ASP.NET controls render as regular html. I believe an <asp:button> renders as a regular button, if I'm not mistaken. You can use a delegated event handler like so:

$('#' + '<%= btnLogin.ClientID %>').on('click', function() {
    msg();
});