//------------------------------------------------------------
 // suppress all error messages and do nothing with them:
 //
 function noErrorMessages () { return true; }
 window.onerror = noErrorMessages;
 
 //------------------------------------------------------------
 // advanced: a full error handler
 //
 function handleError (err, url, line) {
     if (err.indexOf('is not defined') != -1) {
       alert('Oops, something is not defined.\\n' +
              err + '\n' + url + '\nline no: ' + line);
       return true; // error is handled
     }
     else
       return false; // let the browser handle the error
   }
 
 window.defaultOnError = window.onerror; // store default handler
 window.onerror = handleError; // assign own handler
 
 //.. executing my faulty code
 
 window.onerror = window.defaultOnError;  // restore default handler