Narrowing for constant indexed access fails on array getter about typescript

[Andarist]

You can often import npm packages in the playground just fine. It's capable of fetching their types.

I don't see any error here with the nightly version: TS playground. foo.words has number[] type so I'm not sure how undefined has crawled into all of this in your tests. Perhaps you are using noUncheckedIndexedAccess?

This would indeed show the difference in the behavior:
TS 5.4
TS nightly

This, in turn, looks like a correctness improvement.

[RyanCavanaugh]

If this is just an array, I don't see why you need crypto-js as part of the repro. Please provide a minimal example, with config, that shows what's happening

[grant-d]

@RyanCavanaugh yes I am aware of that, but I was unable to find a repro without the package.

@Andarist I think you nailed it - thanks so much, that must be the issue. Not sure what the action is here, I am closing but please re-open as necessary.