Surprising to hear Figma had a custom language for JS. Even more surprising that it was faster than TS. And then they migrate off it onto slower TS! Seems to happen a lot though. Company makes custom stuff early on, gets big, then migrates to something "standard".
It happened in the PHP community as well, facebook being the poster child, but Yahoo also had a fair number of internal optimizations and I saw a few other companies tweak their way to get better perf/security. Then comes a point where the community catches on and has bigger momentum than the company, so it makes sense to move to the standard implementation. I'd kinda see Google's Borg -> k8s move as slightly similar…
PHP and its community were dying by the time FB used it. People here on HN kept talking php down.
In 2014 FB made their own flavour of php with a bunch of perf features, called hack.
Eventually a lot of the perf features hack made its way into php.
FB is still on its own flavour. Php community is still dying.