Refactor ElementListenerMap to use expando properties #18766
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packages/react-dom/src/events/plugins/ModernSelectEventPlugin.js
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Note: Last year, I originally made the change that moved this code to use WeakMaps in #15036.
I recently did some profiling and noticed that we are spending quite a bit of time accessing and setting Maps on
DOMEventListenerMap's WeakMap for each element when using the Modern Event System. The times weren't huge, they were just collectively many moremsthan I would have liked. I profiled switching back to aMapand the times do go down, but then we end up likely leaking by making that change. Why didn't we notice this before? Well I believe it has to do with the fact that we almost always were doing lookups on thedocumentas the WeakMap key, with very few other DOM nodes used as keys. Doing expando lookups ondocumentis about equivalent in performance to doing lookups with a WeakMap (documenthas only a slow path?). Now that we've moved to roots, I'm now seeing a more noticeable perf difference.With all that in mind, I've moved us back to using internal expando properties on DOM nodes instead, which fixes the performance issue I was seeing. I also don't see any regressions with the legacy event system doing this.