Issue

If you have an out of the box SharePoint calendar web part added to a page you might have noticed that using the latest public release version (version 6.6) for either SharePoint On-Premise or for SharePoint Online, when you try accessing that page in Internet Explorer, the page almost instantly freezes and becomes unresponsive.

Reason

Internet Explorer JavaScript engine interprets a DOM event incorrectly and this causes it to enter into an infinite loop, basically freezing the browser and not being able to do anything with it until you close it and launch it again.

Workaround

Using any browser other than Internet Explorer, launch the Theme Builder of the site your page is located on. If you are using SharePoint Online and your site's home page is modern, please make sure that you are launching the Classic Theme Builder.

Once it's opened, Navigate to Utilities > Custom JavaScript. 

Add the following script in the Custom JavaScript input box:

window.addEventListener('DOMSubtreeModified', function (event) {
  event.stopPropagation();
}, true);

Finally click Apply and then Publish, and try opening the page with the calendar web part in Internet Explorer once more. Your page should now load normally and you will be able to interact with the web part as usual.

Related articles:

• Custom JavaScript