Optional
onfulfilled: null | ((value) => TResult1 | PromiseLike<TResult1>)The callback to execute when the Promise is resolved.
Optional
onrejected: null | ((reason) => TResult2 | PromiseLike<TResult2>)The callback to execute when the Promise is rejected.
A Promise for the completion of which ever callback is executed.
Attaches callbacks for the resolution and/or rejection of the Promise.