Promises when all you have are callbacks

Google cloud functions terminate shortly after they finish, so any callbacks and unresolved promises at worst never happen and at best occur intermittently. Their workaround is, if a promise is the return value, they wait to terminate until it’s resolved.

This works great when the API you’re working with actually uses promises, but a lot of third party libraries haven’t caught up with this new feature. Fortunately, Javascript is pretty good at closures, so we can use one to wrap a callback in a Promise:

function awesome_cloud_function(request, response) {
	return new Promise((resolve, reject) => {
		ThirdPartyAPI.function_with_callback(() => { resolve() });
	});
}

This creates a promise that only resolves once the callback finishes. Obviously you should make sure anything that needs to be done in the callback happens before resolving.