[bakkoting]

Formally JavaScript is specified as having TCO as of ES6, although for unfortunate and painful reasons this is spec fiction - Safari implements it, but Firefox and Chrome do not. Neither did QuickJS last I checked and I don't think this does either.

[tracker1]

ES is now ES2025, not ES6/2015. There are still platforms that don't even fully implement enough to shim out ES5 completely, let alone ES6+. Portions of ES6 require buy in from the hosting/runtime environment that aren't even practical for some environments... so I feel the statement itself is kind of ignorant.