I've been looking at this site: https://varvy.com/performance/ and am confused on where blocking css / JS loads are measured. Is it between domLoading
& domInteractive
or between responseEnd
and domLoading
?
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Matt Westlake
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So I finally got a little clarification, and the answer is... "It depends". Looking at http://www.growingwiththeweb.com/2014/02/async-vs-defer-attributes.html
If you use a plain script
tag, it will block inline during the parsing of the html.
If you use DEFER
, the blocking bit will always happen after the HTML is finished rendering.
If you use ASYNC
, the blocking bit can happen at any time (during the HTML rendering, or after depending on how long it takes to download), but BEFORE
ALSO: reference Script Tag - async & defer
So unfortunately there is no easy answer.

Matt Westlake
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