[jacobolus]

You can implement quite a lot of Python's itertools in Javascript without too much trouble. For instance, https://observablehq.com/@jrus/itertools

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.

[raymondh]

Your nice work on the JS itertools port has a todo for a "better tee". This was my fault because the old "rough equivalent" code in the Python docs was too obscure and didn't provide a good emulation.

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

[jacobolus]

Thanks! And thanks, Raymond, for all your hard work over the years!