JSFiddle - React, Tailwind, and code Playground

JavaScript

Promise.prototype.seudofinally = function (foo) {
	return this.then(foo, foo);
}

var p = new Promise((resolve, reject) => {
  setTimeout(() => resolve("resolve"), 1000)
});

p.then(alert).seudofinally(() => alert("final-resolve"));

var p = new Promise((resolve, reject) => {
  setTimeout(() => reject("reject"), 1000)
});

p.then(alert).seudofinally(() => alert("final-reject"));