Javascript Code for Block work of Back space key, Enter key and All Character and Sign keys

function CHKNUM(e,idtxt)

 { 

    var txt = document.getElementById(idtxt);

    if(e.keyCode < 48 || e.keyCode > 57)// && ( keyCode != 8 || e.keyCode != 13))

    {

   

    if(e.keyCode != 13 && e.keyCode != 8)

    { 

      alert("keyCode for the key pressed: " + e.keyCode + "\n");

      alert("Please enter Numbers Only.");

      txt.value="";

      txt.focus();

      return false;

      }

    }

    else

    {

     return true;

    }

 }