I don't know fast it would be if it was done iteratively. But Apple's implementation has negative implications for debuggability: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... https://webkit.org/blog/6240/ecmascript-6-proper-tail-calls-... .

V8 team decided that it's not worth it, since proper stack traces (such as Error.stack) are essential for some libraries, such as Sentry (!). Removing some stack trace info can break some code. Also, imagine you have missing info from the error stack trace in production code running on NodeJS. that's not good. If you need TCO, you can compile that code in WASM. V8 does TCO in WASM.