I just upgraded jQuery from version 2.2.0 (2 years old) to 3.3.1.
Officially this drops support in jQuery for IE 8 and below. In practice … well … jQuery have been slow nuking out old code.
There is an extensive guide about changes from the 2x line to the 3x line at:
https://jquery.com/upgrade-guide/3.0/
We are not the heaviest jQuery consumers so I am not sure how many of these things impact us.
If you notice anything weird and new on the client side, it may relate to this upgrade. Let us know.
https://github.com/discourse/discourse/commit/420739e12c7fbf492f914d2c18ce73d501712c98