perf(synthetic-shadow): micro-optimize MutationObserver #3729
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nolanlawson
commented
Sep 22, 2023
| characterData: true, | ||
| childList: true, | ||
| subtree: true, | ||
| }); |
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The most expensive MutationObserver is actually this one. It's very expensive because it gets triggered for mutations inside of a shadow root that it doesn't have access to, so the results have to be filtered out.
nolanlawson
commented
Sep 22, 2023
| } | ||
| } | ||
| } | ||
| return result; |
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This diff is hard to read, but there are 2 small changes here:
- Convert
ArrayReduceinto a regular for-loop (this is the bulk of the improvement). - Lazily access properties from the
recordrather than all at once (this is maybe a 1% perf improvement – apparently the browser does some work when you call these getters).
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Details
A small micro-optimization for our
MutationObserverpolyfill.Also adds a benchmark, which is improved by 2%-6%:
I have other ideas for improvements, but I'm keeping this PR simple to make it easier to review.
Does this pull request introduce a breaking change?
Does this pull request introduce an observable change?