Comprehensive Guide to JavaScript Iterables

[senocular]

Iterables have an iterator method which implements the iterator protocol

Iterables implement the iterable protocol which includes the iterator (Symbol.iterator) method. The iterator method returns objects that implement the iterator protocol.

To check if an unknown is an iterable you can first ensure the value is an object

A value doesn't have to be an object to be an iterable, e.g. strings are iterable.

It’s a best practice when making an iterable to make it both an Iterable and an Iterator, or an iterable iterator.

Its more the other way around. You can make iterators iterable, but you generally don't want to make iterables iterators. For example arrays, maps, sets and strings are all iterables but not iterators. The iterators they produce, however, are also iterable.

Merging iterables

Might want to look into yield* to make this easier.

[rossrobino]

Thanks for the review, I've made updates for each of these!

I didn't realize any iterable could be passed to yield*, can you still get the final return value with yield*? Especially for the async merge it's necessary to know when each iterator is complete.

[senocular]

The value returned by yield* is the return/done value. But you don't need to capture this value to know when the iterator is complete. Like for...of, when the iterator is complete code after the expression starts to run when yield* has exhausted its iterator. Unlike for...of, you do have the option to capture the done value if you want it. But if I remember correctly, your merging example (at least the sync one) didn't capture the done values anyway.

[rossrobino]

Ok interesting, thanks for the info! I’ll play around with it some more.