[technion]

Es6 arrow functions are a good example of this. They have been around for a long time and work in most browsers, but people learned they need babel to transpile them out for internet Explorer. People dropped ie support but the knowledge "we need babel for browser compatibility " remained an entrenched fact.

[WorldMaker]

Yeah, it's relevant to remember that arrow functions were defined in ES2015 (eight years ago) and like I said most browsers people are using are caught up through at least ES2021. The nice thing about the ES2015 year-based nomenclature (as opposed to the people still calling it "ES6") is that you can do a quick reasonable first approximation of caniuse statistics off hand with "is that standard at least two years old?" Arrow functions are old.