Google is good, really good, at rendering JavaScript these days, even pretty inefficient JavaScript. So much so that Martin Splitt from Google said the only time you really need to worry about CPU usage being a problem is when it is such a big issue that your users CPUs get so hot the fans on the computer sounds like it is going to "lift off."
It makes sense... Have you ever gone to a web site and the whole page locks up, you hear your computers fans start whirling? I have and I do my best to close that page as soon as possible. Those are the types of pages Google might have problems with.
Here is the Twitter stream where Martin Splitt from Google says this:
Since @Google announced that it will cut off loading scripts that take too much CPU -- how are #SEO Folks checking the CPU (ie which tools and reports) and is there a known threshold? https://t.co/EUuUhC3b5i@jennyhalasz @glenngabe @AlanBleiweiss @bart_goralewicz @Kevin_Indig
— Kristine Schachinger (@schachin) December 3, 2019
Ah, the slide is taken out of context again.
— Martin Splitt @ 🇺🇸 #TechSEOBoost #Boston (@g33konaut) December 4, 2019
There's no explicit or strict limit. As long as your website doesn't take stupid amounts of time to get ready with its JS, it ain't a problem. If it's a problem, the user impact is eclipsing any potential SEO problems with that.
Don't sweat it. If you have a CPU problem, your users will probably notice it before it becomes a SEO issue.
— Martin Splitt @ 🇺🇸 #TechSEOBoost #Boston (@g33konaut) December 4, 2019
Well, if a website locks up the browser / your computer and the fans make it sound like it might lift off, that's when you need to worry about the CPU.
— Martin Splitt @ 🇺🇸 #TechSEOBoost #Boston (@g33konaut) December 4, 2019
No, that's what I'm trying to get across here :)
— Martin Splitt @ 🇺🇸 #TechSEOBoost #Boston (@g33konaut) December 4, 2019
So cool it, literally, cool it. :)
Forum discussion at Twitter.