Disclaimer: this code was written several years ago with few downstream users, not all of these are super high performing, and they have not been super extensively tested.
Here is an update that should be much easier to convert to JS:
def tee(iterable, n=2):
iterator = iter(iterable)
shared_link = [None, None]
return tuple(_tee(iterator, shared_link) for _ in range(n))
def _tee(iterator, link):
try:
while True:
if link[1] is None:
link[0] = next(iterator)
link[1] = [None, None]
value, link = link
yield value
except StopIteration:
return