Indexed array access type is not possibly undefined with noUncheckedIndexAccess enabled

[BrianESimon]

Bug Report

🔎 Search Terms

noUncheckedIndexAccess, array

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about noUncheckedIndexAccess

⏯ Playground Link

Playground link with relevant code

💻 Code

With noUncheckedIndexAccess enabled:

const arr: string[] = [];

type IncorrectArrayType = typeof arr[0]; // string

// there's a workaround, but it involves runtime overhead
const correct = arr[0];
type CorrectArrayType = typeof correct; // string | undefined

🙁 Actual behavior

Indexing an array type doesn't include undefined with noUncheckedIndexAccess enabled

🙂 Expected behavior

IncorrectArrayType should be string | undefined

[whzx5byb]

This is by design and you could find more details in #39560. See the last section: Design Point: What's the type of T[number] / T[string].

[BrianESimon]

Okay. Thank you for the link