method Promise.then Private Promise.then<TResult1 = T,TResult2 = never,>(onfulfilled?: ((value: T) => TResult1 | PromiseLike<TResult1>) | undefined | null,onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | undefined | null,): Promise<TResult1 | TResult2> Attaches callbacks for the resolution and/or rejection of the Promise. Type Parameters TResult1 = T TResult2 = never Parameters optional onfulfilled: ((value: T) => TResult1 | PromiseLike<TResult1>) | undefined | null The callback to execute when the Promise is resolved. optional onrejected: ((reason: any) => TResult2 | PromiseLike<TResult2>) | undefined | null The callback to execute when the Promise is rejected. Return Type Promise<TResult1 | TResult2> A Promise for the completion of which ever callback is executed.