js: ast.GoExpr support using promises on JS backend (#12749)

vlib/builtin/js/promise.js.v

@@ -0,0 +1,81 @@
+module builtin
+
+pub interface JS.Promise {
+	then(onFullfilled JS.Any, onRejected JS.Any)
+	catch(onCatch JS.Any) JS.Promise
+	finally(callback JS.Any) JS.Promise
+}
+
+[use_new]
+pub fn JS.Promise.prototype.constructor(JS.Any) JS.Promise
+pub fn JS.Promise.reject(JS.Any) JS.Promise
+pub fn JS.Promise.resolve(JS.Any) JS.Promise
+pub fn JS.Promise.race(JS.Array) JS.Promise
+
+// The Promise object represents the eventual completion (or failure)
+// of an asynchronous operation and its resulting value.
+pub struct Promise<T, E> {
+mut:
+	promise JS.Promise [noinit]
+}
+
+pub fn promise_new<T, E>(executor fn (resolve fn (T), reject fn (E))) Promise<T, E> {
+	promise := JS.Promise.prototype.constructor(executor)
+	return Promise<T, E>{promise}
+}
+
+pub fn (p Promise<T, E>) then(on_fullfilled fn (T), on_rejected fn (E)) {
+	p.promise.then(on_fullfilled, on_rejected)
+}
+
+// catch method returns a Promise and deals with rejected cases only.
+pub fn (p Promise<T, E>) catch(callback fn (error JS.Any)) Promise<T, E> {
+	promise := p.promise.catch(callback)
+	return Promise<T, E>{promise}
+}
+
+pub fn (p Promise<T, E>) finally(callback fn ()) Promise<int, int> {
+	promise := p.promise.finally(callback)
+	return Promise<int, int>{promise}
+}
+
+// reject<E> returns promise which was rejected because of specified error
+pub fn promise_reject<E>(error E) Promise<int, E> {
+	promise := JS.Promise.reject(error)
+	return Promise<int, E>{promise}
+}
+
+// resolve<E> returns promise which was resolved with specified value
+pub fn promise_resolve<T>(result T) Promise<T, int> {
+	promise := JS.Promise.resolve(error)
+	return Promise<T, int>{promise}
+}
+
+// race returns returns a promise that fulfills or rejects as soon as one of
+//  the promises in an iterable fulfills or rejects, with the value or reason from that promise.
+pub fn promise_race<T, E>(promises []Promise<T, E>) Promise<T, E> {
+	promises_ := JS.Array.prototype.constructor()
+
+	for elem in promises {
+		promises_.push(elem.promise)
+	}
+
+	promise := JS.Promise.race(promises_)
+	return Promise<T, E>{promise}
+}
+
+pub fn JS.Promise.all(JS.Array) JS.Promise
+pub fn JS.Promise.allSettled(JS.Array) JS.Promise
+
+/*
+pub type JsAny = JS.Any
+
+// all takes an iterable of promises as an input, and returns a single Promise that resolves to an array of
+// the results of the input promises
+pub fn all(array []JS.Promise) Promise<JS.Array, js.promise.JsAny> {
+	mut promise := JS.Promise(JS.Any(voidptr(0)))
+	#promise = Promise.all(array.arr.arr);
+
+	return Promise<JS.Array,JsAny>{promise}
+}
+*/