Don't emulate bubbling of the scroll event #19464
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React Core Team
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What does onScrollCapture do? |
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Not sure what you mean. It does regular capturing? That mirrors the browser behavior AFAIK. |
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Meaning, it would currently capture at the root and call React capture listeners. |
trueadm
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Jul 27, 2020
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I'm thinking this is worth putting behind a flag. Kind of risky. |
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I'm gonna land this behind a flag so we can quickly roll back if something's broken. |
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Currently, scroll event is somewhat broken on master.
This will fire both handlers if we scroll the child:
But this will not fire the parent handler if we scroll the child:
In other words, bubbling the scroll event currently doesn't work if the event target itself doesn't have a React listener.
This is a regression in the modern system.
Possible Fixes
This is based on @trueadm's writeup.
Option 1: Add native
scrollhandler to everydivso that we can't "miss" the event — whether it has a React handler or not. This is a similar strategy we use for other events that don't bubble in the browser (e.g.toggle,invalid,play, etc). However, for those cases, we know which elements need it (e.g.audioandvideo). Adding ascrolllistener to every singledivseems untenable. So this is ruled out for performance reasons.Option 2 (Breaking Change): Stop emulating bubbling for
onScroll. It it confusing anyway (Bug: Strange onScroll behaviour when child editing #19156, Strange onScroll behaviour #15723). This is what this PR does. The downside is that now this event is special and different from all others.Option 3 (Even Bigger Breaking Change): Stop emulating bubbling for all events that don't bubble in the browser. This includes
invalid,load,toggle,close,cancel, and media events. We could consider this but it's a bigger breaking change. Arguably, some of them, likeonInvalid, are actually useful and not too confusing to bubble. So I think this needs to wait until 18.Option 4 (Status Quo): We could go back to React 16 behavior, which attaches
onScrollin the capture phase. That would solve the current inconsistency, but wouldn't be in line with our strategy for how nested Reacts should work. It also wouldn't solve the problem that bubblingonScrollis inherently confusing.