See before: https://gist.github.com/esphen/805e0ccd14e8df37b5a504930b682a63#file-esnext-ts-before-js

esnext-ts.js

var n = (function() {
	function n() {}
	return (
		(n.prototype.then = function(r, e) {
			var o = new n(),
				i = this.s;
			if (i) {
				var u = 1 & i ? r : e;
				if (u) {
					try {
						t(o, 1, u(this.v));
					} catch (n) {
						t(o, 2, n);
					}
					return o;
				}
				return this;
			}
			return (
				(this.o = function(n) {
					try {
						var i = n.v;
						1 & n.s ? t(o, 1, r ? r(i) : i) : e ? t(o, 1, e(i)) : t(o, 2, i);
					} catch (n) {
						t(o, 2, n);
					}
				}),
				o
			);
		}),
		n
	);
})();
function t(r, e, o) {
	if (!r.s) {
		if (o instanceof n) {
			if (!o.s) return void (o.o = t.bind(null, r, e));
			1 & e && (e = o.s), (o = o.v);
		}
		if (o && o.then) return void o.then(t.bind(null, r, e), t.bind(null, r, 2));
		(r.s = e), (r.v = o);
		var i = r.o;
		i && i(r);
	}
}
function r(t) {
	return t instanceof n && 1 & t.s;
}
function e(n, t) {
	try {
		var r = n();
	} catch (n) {
		return t(!0, n);
	}
	return r && r.then
		? r.then(t.bind(null, !1), t.bind(null, !0))
		: t(!1, value);
}
function o(n) {
	var t = 'function' == typeof Symbol && n[Symbol.iterator],
		r = 0;
	return t
		? t.call(n)
		: {
				next: function() {
					return (
						n && r >= n.length && (n = void 0), { value: n && n[r++], done: !n }
					);
				},
		  };
}
function i(n) {
	if (!Symbol.asyncIterator)
		throw new TypeError('Symbol.asyncIterator is not defined.');
	var t,
		r = n[Symbol.asyncIterator];
	return r
		? r.call(n)
		: ((n = o(n)),
		  (t = {}),
		  e('next'),
		  e('throw'),
		  e('return'),
		  (t[Symbol.asyncIterator] = function() {
				return this;
		  }),
		  t);
	function e(r) {
		t[r] =
			n[r] &&
			function(t) {
				return new Promise(function(e, o) {
					(function(n, t, r, e) {
						Promise.resolve(e).then(function(t) {
							n({ value: t, done: r });
						}, t);
					})(e, o, (t = n[r](t)).done, t.value);
				});
			};
	}
}
var u = function() {
	try {
		var o,
			u,
			f,
			c,
			h = [],
			v = e(
				function() {
					return (function(n, t) {
						try {
							var r = n();
						} catch (n) {
							return t(n);
						}
						return r && r.then ? r.then(void 0, t) : r;
					})(
						function() {
							o = i([1, 2]);
							var e = (function(e, o, i) {
								for (var u; ; ) {
									var f = e();
									if ((r(f) && (f = f.v), !f)) return c;
									if (f.then) {
										u = 0;
										break;
									}
									var c = i();
									if (c && c.then) {
										if (!r(c)) {
											u = 1;
											break;
										}
										c = c.s;
									}
									if (o) {
										var h = o();
										if (h && h.then && !r(h)) {
											u = 2;
											break;
										}
									}
								}
								var v = new n(),
									a = t.bind(null, v, 2);
								return (
									(0 === u ? f.then(s) : 1 === u ? c.then(l) : h.then(d)).then(
										void 0,
										a,
									),
									v
								);
								function l(n) {
									c = n;
									do {
										if (o && (h = o()) && h.then && !r(h))
											return void h.then(d).then(void 0, a);
										if (!(f = e()) || (r(f) && !f.v)) return void t(v, 1, c);
										if (f.then) return void f.then(s).then(void 0, a);
										r((c = i())) && (c = c.v);
									} while (!c || !c.then);
									c.then(l).then(void 0, a);
								}
								function s(n) {
									n
										? (c = i()) && c.then
											? c.then(l).then(void 0, a)
											: l(c)
										: t(v, 1, c);
								}
								function d() {
									(f = e())
										? f.then
											? f.then(s).then(void 0, a)
											: s(f)
										: t(v, 1, c);
								}
							})(
								function() {
									return !!Promise.resolve(o.next()).then(function(n) {
										return !(u = n).done;
									});
								},
								void 0,
								function() {
									h.push(u.value);
								},
							);
							return e && e.then ? e.then(function() {}) : void 0;
						},
						function(n) {
							f = { error: n };
						},
					);
				},
				function(n, t) {
					function r(r) {
						if (n) throw t;
						return t;
					}
					var i = e(
						function() {
							var n = (function() {
								if (u && !u.done && (c = o.return))
									return Promise.resolve(c.call(o)).then(function() {});
							})();
							return n && n.then ? n.then(function() {}) : void 0;
						},
						function(n, t) {
							if (f) throw f.error;
							if (n) throw t;
							return t;
						},
					);
					return i && i.then ? i.then(r) : r();
				},
			);
		return Promise.resolve(
			v && v.then
				? v.then(function(n) {
						return h;
				  })
				: h,
		);
	} catch (n) {
		return Promise.reject(n);
	}
};
u().then(console.log), (module.exports = u);
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