AI solution for TypeScript puzzle on BFE.dev
24. implement LengthOfString<T>

Solution:

type LengthOfString<T extends string> = T['length'];

type A = LengthOfString<'BFE.dev'> // 7
type B = LengthOfString<''> // 0

Explanation:

In this solution, we define a generic type T that extends the string type, and then use the built-in length property of the string type to get the length of the string. We do this by using an index type query with T['length'], which fetches the length property of the T type.

Then we use this LengthOfString<T> type to get the length of the given string. For example, the LengthOfString<'BFE.dev'> would return 7 and LengthOfString<''> would return 0.