tabledrag.js falls unusable on large menus (e.g. 150+ menu items) on older browsers. (e.g. IEs / Edge, some reported Firefox also).
After a quick debugging, I found that executed a very expensive function on MouseEvent. @see below:
tabledrag.js is one of the largest JS lib in Core. It's about 1600 lines. Any huge refactoring seems impossible at the moment. It required a lot of human time to write JSTests and human testing & reviews.
After some thoughts, I decided to add a simple DEBOUNCE function to the MouseEvent. On my testing, it works much better.
Note: It still not perfect. DOM rendering is also slow on older browsers. We could do further improvement on follow-ups
(I suggested to skip JSTests on tabledrag.js of this simple patch.)
- Human Testing on different browsers
- Review patches
(Hints: Using Devel module to gen menu items)
User interface changes
Data model changes