If you’re really trying to squeeze out every last drop of “time-to-first render” performance, keep the script and other page resources below ~14KB so they can be sent within the first TCP roundtrip. 🤓
We came across this topic in this article from Wikimedia who have been optimizing their JS payloads to fit into 2x14KB chunks over the last year. By reducing their JS from 36KB to 24, they say they are […] saving 4.3 Terabytes a day of data bandwidth for our users’ page views.
Version 4 of the Google PageSpeed documentation also references the “magic” 14KB threshold.