Should throw if falsey key value exists

[Donavon West]

In your example, if foo.d is already set to say 5, it throws. I would expect that. However, if it is 0 (or anything falsey), it paves over the falsey value.

{a: 1, b: 2, d: 0}
//=> { a:1, b:2, d:{ e:{ f:'hello' } } };

A possible fix is:

x = o[keys[i]] === undefined ? {} : o[keys[i]];

[Luke Edwards]

Ah, right, good catch~! I'll fix this, but we should also be paving on null value too.

Slightly unrelated, but thoughts about not throwing if a value exists? Instead, would silently break & exit.

[Donavon West]

I wouldn't pave over a null as it is an actual value.

I'm a big fan of throwing when there is an exception. Hiding/masking the problem will make it harder to track down the root cause.

Actually, you might want to use this instead:

x = keys[i] in o ? o[keys[i]] : {};

[Luke Edwards]

That'd throw immediately for anything that isn't already an object, including undefineds 😆 That's probably what you want, except for the latter.