Popper.js added to Drupal core to replace jQuery UI Position

Introduction

jQuery UI Position will be deprecated due to jQuery UI no longer being supported. The OpenJS Foundation lists jQuery UI as an Emeritus project in https://openjsf.org/projects/ which is described as:

Emeritus projects are those which the maintainers feel have reached or are nearing end-of-life

PopperJS was evaluated and selected to replace jQuery UI Position in Drupal core.

Changes in Drupal core

• The Quick Edit module no longer uses jQuery UI Position to position its toolbar.
• There are no changes to the core/jquery.ui.position library since it is a dependency of other jQuery UI libraries that are still used by core (including Dialog and Autocomplete).

Changes for contributed modules and themes

It is recommended that modules or themes that currently depend on jQuery UI Position directly update their code to depend on Popper.js instead. Review the Popper.js documentation, and see the changes in the QuickEdit module in #3074267: Replace jQuery UI position() with PopperJS for an example of how this has been implemented in Drupal. jQuery UI Position will be removed from Drupal core in a future release.