Tail call optimization isn't just for recursive tail call optimization (though that is the most common scenario!).

It simply refers to 'unrolling' that function call, so a new function doesn't need to be added to the stack.

JS's iteration methods aren't currently recursive, at least in V8[0]. But that's probably due to lack of TCO!

0. https://github.com/v8/v8/blob/master/src/array.js#L1378