function whichKey(e) {
if (window.event) {
    code=event.keyCode;
    }
else {
    code= e.which;
    }
switch (code) {
   case 98 : // b
      history.go(-1);
      break;
   case 102 : // f
      history.go(1);
      break;
   case 112 : // p
      window.print();
      break;
   default :
      alert("Unused key");
    }
}
document.onkeypress=whichKey;