Are functions in JavaScript tail-call optimized?

Question

I have been trying to understand Tail call optimization in context of JavaScript and have written the below recursive and tail-recursive methods for facto

Answer 1

In theory yes. As the other answer states.

In practice though, as of July 2017, No. Only Safari supports it.

Javascript ES6 (ES2015) compatability: https://kangax.github.io/compat-table/es6/