@vendredix/promise/lib/then-shortcuts.js

Native promise extensions

"use strict";
const utils = require("./utils");

function promiseReturn(val) {
  return this.then(() => val);
}

function promiseThrow(val) {
  return this.then(() => {throw val});
}

function promiseFinally(onFinally) {
  if (typeof onFinally !== "function") {
    throw new TypeError("onFinally is not a valid function");
  }

  const C = utils.speciesConstructor(this, Promise);

  // https://github.com/tc39/proposal-promise-finally/blob/master/polyfill.js
  return Promise.prototype.then.call(
    this,
    x => new C(resolve => resolve(onFinally())).return(x),
    e => new C(resolve => resolve(onFinally())).throw(e),
  )
}

utils.definePrototypeHelper("return", promiseReturn);
utils.definePrototypeHelper("throw", promiseThrow);
utils.definePrototypeHelper("finally", promiseFinally);