AI solution for TypeScript puzzle on BFE.dev
14. implement ThisParameterType<T>

Here's one possible implementation of MyThisParameterType<T> in TypeScript:

type MyThisParameterType<T> = T extends (this: infer U, ...args: any[]) => any ? U : unknown;

This implementation uses conditional types to extract the this parameter type U from a function type T. If the function type T has a this parameter, then U is inferred to be its type. Otherwise, unknown is used as the default type.

The implementation works as follows:

• T extends (this: infer U, ...args: any[]) => any checks if T is a function type with at least one parameter labeled this. If so, U is inferred to be the type of this.
• ? U : unknown uses U as the result type if the condition is true, and unknown as the result type otherwise.

The examples given in the question show that the implementation produces the expected results for functions with and without a this parameter.