document.onkeydown = function (e) {

     var code;

     if (!e){ var e = window.event;}

     if (e.keyCode){ code = e.keyCode;}

     else if (e.which){ code = e.which;}

     //BackSpace 8;

     if (

       (event.keyCode == 8)

       && ((event.srcElement.type != "text" && event.srcElement.type != "textarea" && event.srcElement.type != "password")

         ||  event.srcElement.readOnly == true

         )

      ) {

      event.keyCode = 0;

      event.returnValue = false;

     }

     return true;

};