Observable.from should throw primitive iterables (strings)

[benlesh]

Along with how Iterator helpers behave, if a user passes a string, even though it's an iterable, it's likely an error. We should throw a TypeError in that case.

Observable.from('some string'); // TypeError

[bakkot]

I think you misread my comment (which was not all that clear, sorry). Iterator.from does not throw when given a string. This makes it different from flatMap, which does throw when the mapper returns a string, even though strings are iterable.

See discussion in tc39/proposal-iterator-helpers#244.

[petamoriken]

FYI: ReadableStream.from rejects string whatwg/webidl#1397

[ljharb]

If someone is intentionally passing a string into an X.from method, they explicitly want to convert a string into an X. I think this is the one case where an iterable string must be accepted.

[flensrocker]

Can a usecase be returning a string from the catch operator?
How should I do this if Observable.from throws on a string? Or can I just return the string?
(having rxjs of("...") in mind)

[domfarolino]

I'm sold on ensuring Observable.from("string") works the same as Observable.from(Object("string")) does today, by basically adding special handling like https://github.com/tc39/proposal-iterator-helpers/pull/250/files did for Iterator helpers. I'll ensure that this makes it into #160, and I'll close this issue.