react-resizer appears to be okay at tracking state, but it often desyncs from reality. re-resizer is more maintained and more broadly used (160k downloads vs 110k), and appears to generally do a better job of tracking the cursor.
The new library has some oddities though, such as deltas, touch support (hence the polyfill), and calling handles "Enable".
For https://github.com/vector-im/riot-web/issues/14022
15b6a273c9