Google Bot Crawl Debugging

error.js

window.onerror = function (message, url, lineNo, colNo, error) {

   console.log(arguments);

   let container = document.createElement('div');

   container.style.color = 'red';
   container.style.position = 'fixed';
   container.style.background = '#eee';
   container.style.padding = '2em';
   container.style.top = '1em';
   container.style.left = '1em';

   let msg = document.createElement('pre');
   msg.innerText = [
      'Message: ' + message,
      'URL: ' + url,
      'Line: ' + lineNo,
      'Column: ' + colNo,
      'Stack: ' + (error && error.stack)
   ].join('\n');

   container.appendChild(msg);

   document.body.appendChild(container);
};