How to create KeyPress Event in asp.net page

If you are looking for something like below,
Create a JS function and call that on ASP control onkeypress event

function LettersWithSpaceOnly(evt) {
        evt = (evt) ? evt : event;
        var charCode = (evt.charCode) ? evt.charCode : ((evt.keyCode) ? evt.keyCode :
    ((evt.which) ? evt.which : 0));
        if (charCode > 32 && (charCode < 65 || charCode > 90) &&
        (charCode < 97 || charCode > 122)) {
            return false;
        }
        return true;
    }

<asp:textbox id="txtFN" runat="server" width="100%" maxlength="25" onkeypress="return LettersWithSpaceOnly(event);" xmlns:asp="#unknown">


Happy Coding!!!