Defer CLS logic until after onFCP callback #297
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tunetheweb
approved these changes
Jan 9, 2023
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@philipwalton @tunetheweb does this adjustment have an impact on concrete CLS numbers? |
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It does not, other than cases affected by the bug outlined in this comment: #180 (comment) |
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This PR fixes #180 by removing some of the logic that would listen and keep track of whether or not FCP had fired, and instead just wraps all of the
onCLS()logic inside of anonFCP()call (and ensuring the logic only runs the first timeonFCP()is invoked).The "ensuring the logic only runs the first time
onFCP()is invoked" bit is accomplished by introducing a newrunOnce()utility function, and I took this opportunity to refactor some of the other code to make use of that. The end result was a little bit of byte savings, so it was worth it.Also, #180 caught a bug in the library where, if the library was lazy-loaded, CLS wouldn't properly be reported when
reportAllChangeswas true. I realized there were no tests to ensure things work when the library is lazy-loaded, so I added some, which also required refactoring some of the testing logic.Lastly, this PR also updates a bit of the formatting style (continuing what was done in #288) since some of that was auto-formatting unrelated files anyway (not sure why, but seems to be fine now).