Promise interface with Reject ReturnType

IPromise.ts

interface IPromise<T, U> {
  then<TResult1 = T, TResult2 = never>(
    onfulfilled?:
      | ((value: T) => TResult1 | PromiseLike<TResult1>)
      | undefined
      | null,
    onrejected?:
      | ((reason: U) => TResult2 | PromiseLike<TResult2>)
      | undefined
      | null
  ): IPromise<TResult1 , TResult2>;
  catch<TResult = never>(
    onrejected?:
      | ((reason: U) => TResult | PromiseLike<TResult>)
      | undefined
      | null): Promise<TResult>;