Function To Validate Only Alphabet allowed in JavaScript

function fnAlphabet(e)
{
    var code = e.keyCode ? event.keyCode : e.which ? e.which : e.charCode;
    //alert(code);
    if ((code >= 65 && code <= 90)||(code >= 97 && code <= 122) || code==46 || code==8 || code==17 || code==127 || code==9 || code==16 || code==37 || code==38 || code==39 || code==40)
    {
        checknos = true;
        return (checknos);
    }
    else
    {
        checknos= false;           
        alert("Only Alphabates Allowed !");       
        return (checknos);        }
}