I was wondering if anybody knows how to get rid of this following reflow, apparently triggered by analytics, or where to discuss about it on github ? thanks
2 Answers
This document claims that a reflow is triggered for clientWidth and clientHeight even when they are being read (not just when set). However the author also points out that
Reflow only has a cost if the document has changed and invalidated the style or layout. Typically, this is because the DOM was changed [...]
which the analytics script does not do. So there seems to be a reflow, but I doubt that it come with a big performance penalty. In any case you will not get rid of this.
The article also links to a lot of other posts that discuss forced reflow issues.
Thanks for your answer. I believe this warning was accurate and need to be addressed as stated in https://developers.google.com/web/fundamentals/performance/rendering/avoid-large-complex-layouts-and-layout-thrashing#avoid-forced-synchronous-layouts .
By following up the callstack I realized that one of our script was adding a class to the body after first rendering and this was apparently the cause of the reflow. I still do not really get why analytics is the script raising this warning in Performance tab, I guess it might watch body size change.
Best regards
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