TCO is a runtime feature that enables code authors to write functions that call out to other functions in such a way that the stack size is not increased. If you’ve ever crossed the `RangeError: Maximum Call Stack Size Exceeded` error, it’s possible that the executed code could’ve benefitted from TCO. TCO is especially invaluable for writing recursive functions (without it, recursion is almost always a bad idea, IMHO).

TCO is technically in the ECMAScript specification (since 2015) but hasn’t been implemented across browsers or runtimes (with a few exceptions).

Dr. Axel has written a good explainer of TCO in the context of Javascript here https://2ality.com/2015/06/tail-call-optimization.html