Throttle UI update event

[mlewand]

📝 Provide a description of the improvement

The update event is sometimes called very frequently, examples include:

• image resize it fires on each image resize redraw,
• dragging content over the editable (I believe it's due to caret showing the potential drop placement),
• simply holding right arrow key (to keep moving selection),
• column resize

It's similar to what we had in browsers couple of years ago with the scroll event, which in the end got throttled too.

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[Reinmar]

I wonder whether the source event should be throttled or the consumer should throttle their listeners?

IDK the full story behind the scroll event, but I'd expect:

• people blindly plugging into it with heavy code
• the event itself being deep in the browser engine's internal, possibly in another thread that takes care of rendering, hence generating a ton of complexity when trying to sync with another thread and a blocking JS event handlers

The former is a case for us too perhaps, but the latter (I guess?) has a lower impact on us.

With throttling the original event, I have a problem that there may be code that actually needs an unthrottled one.

Maybe we should have:

• EditorUI#update throttled
• EditorUI#updateUnsafeSynchronous not throttled

BTW, am I right that moving listeners of #update to a throttled event will ensure that if a UI-related logic throws, it does not interfere with the rest of the code (error goes into the global scope)?

[Witoso]

Pardon my ignorance, what's the impact, and what problems are caused by the update being not throttled? Could there be some other solution to it?

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