JS Promises for GameMaker 2024.14

Download the .yymps

This library is "made" by me, Juju Adams, but it is heavily based on prior work by YellowAfterlife. His work is, in turn, based on a JS Promise polyfill by Taylor Hakes.

GameMaker does not allow using built-in function names as variable names, so:

• new Promise ➜ Promise()
• promise.then ➜ PromiseThen()
• promise.catch ➜ PromiseCatch()
• promise.finally ➜ PromiseFinally()
• Promise.all ➜ PromiseAll()
• Promise.allSettled ➜ PromiseAllSettled()
• Promise.any ➜ PromiseAny()
• Promise.race ➜ PromiseRace()
• Promise.reject ➜ PromiseReject()
• Promise.resolve ➜ PromiseResolve()

GameMaker also does not allow naming methods same as keywords, therefore:

• .then ➜ .Then
• .catch ➜ .Catch
• .finally ➜ .Finally
• .all ➜ .All

I found it helpful to create some new promise types to make the library easier to work with. PromiseTimeout() and PromiseDelay() will wait an amount of real time before completing the promise (rejection in the case of PromiseTimeout(), resolve in the case of PromiseDelay()).

To make integration with native GameMaker code easier, I added PromiseCustom() which exposes the resolve and reject functions as public methods. You should call these functions with the return value when whatever process you're doing has completed. You can get a promise made with PromiseCustom() track a particular scope (a struct or an instance) to ensure that promises always fire off even if your game does something unexpected.

Can also be found in the sample project, along with supporting scripts.

Featuring a custom call_later_ext().

Promise(
	function(_resolve, _reject) {
	    if (random(1)) {
			call_later_ext(250, _resolve, "hello!");
	    } else {
			call_later_ext(250, _reject, "bye!");
	    }
	}
).Then(
	function(_value) {
		trace("resolved!", _value);
	},
	function(_value) {
		trace("failed!", _value);
	}
);

PromiseAll([
	PromiseResolve(3),
	42,
	Promise(
		function(_resolve, _reject) {
		    call_later_ext(100, _resolve, "hello!");
		}
	)
]).Then(
	function(_values) {
		trace(_values);
	}
);

Promise_http_get("https://yal.cc/ping").Then(
	function(_value) {
		show_debug_message($"success = {_value.result}");
		return Promise_http_get("https://yal.cc/ping");
	}
).Then(
	function(_value) {
		show_debug_message($"success2 = {_value.result}");
	}
).Catch(
	function(_error) {
		show_debug_message($"failed = {_error}");
	}
);

• PascalCase naming which is not to everyone's taste
• Have to "promisify" built-in functions, but made easier by PromiseCustom()
• Original JS library's unit tests have not been ported