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; 
};