patrick-fs

Sentry.init({
    dsn: 'your Sentry DSN', // if you're logged into Sentry, you can find your DSN in ths sample code on this page: https://docs.sentry.io/platforms/javascript/react/
    beforeSend(event, hint) {
      const error = hint.originalException;
      event.extra = event.extra || {};

      var _fs = window[window._fs_namespace]];
        
      if (typeof _fs !== 'function') {
        event.extra.fullstory = 'FullStory is not installed';

paulirish

What forces layout / reflow

All of the below properties or methods, when requested/called in JavaScript, will trigger the browser to synchronously calculate the style and layout*. This is also called reflow or layout thrashing, and is common performance bottleneck.

Generally, all APIs that synchronously provide layout metrics will trigger forced reflow / layout. Read on for additional cases and details.

Element APIs

Getting box metrics

• elem.offsetLeft, elem.offsetTop, elem.offsetWidth, elem.offsetHeight, elem.offsetParent