$ JS Alert On Error

window.onerror = function(msg, url, line, col, error) {
  // Note that col & error are new to the HTML 5 spec and may not be
  // supported in every browser.  It worked for me in Chrome.
  var extra = !col ? '' : '\ncolumn: ' + col;
  extra += !error ? '' : '\nerror: ' + error;
  alert("Error: " + msg + "\nurl: " + url + "\nline: " + line + extra);
  var suppressErrorAlert = true;
  // If you return true, then error alerts (like in older versions of
  // Internet Explorer) will be suppressed.
  return suppressErrorAlert;
};