Simple implementation of async/await workflow with generators and yield.

async-await-with-generators.js

function doSomething(){
	return Promise.resolve(73);
}

function timeout(ms){
	return new Promise((resolve) => setTimeout(resolve, ms, ms));
}

function asyncFlow(generatorFunc){
	const generator = generatorFunc();
	function callGeneratorSafeWithParam(param = undefined, throws = false){
		try{
			const { value, done } = throws ? generator.throw(param) : generator.next(param);
			const promise = value instanceof Promise ? value : Promise.resolve(value);
			if(done)
				return promise;
			else
				return promise.then(resultCallback, errCallback);
		}catch(err){
			return Promise.reject(err);
		}
	}
	function errCallback(err){
		return callGeneratorSafeWithParam(err, true);
	}
	function resultCallback(res){
		return callGeneratorSafeWithParam(res);
	}

	return callGeneratorSafeWithParam(undefined);
}

asyncFlow(function* test(){
	const value = yield doSomething();
	console.log('Got result of the promise:', value);

	console.log('Waiting 3 seconds before finishing.');
	const time = yield timeout(3000);
	console.log('Waiting time in ms:', time);

	// extra wait just for fun
	yield timeout(1000);
	return value;
}).then((res) => console.log('Should print the value from doSomething(73):', res));

asyncFlow(function* test2(){
	throw new Error('wtf');
}).catch((err) => console.log('Should end with wtf error:', err));

asyncFlow(function* test3(){
	// should drop in to global unhandled promise rejection
	Promise.reject('first');
	console.log('--- Should see this.');
	// should be returned as a result of this function(promise rejection)
	yield Promise.reject('second');
	console.log('--- Should not see this.');
}).catch((err) => console.log('Should fail on the second error:', err));

asyncFlow(function* test4(){
	try{
		yield Promise.reject('wut');
		console.log('---- Should not see this.');
	}catch(err){
		console.log('---- Should see this.');
	}
	console.log('---- Should see this aswell.');
	return 73;
}).then((res) => console.log('Response of test4:', res), (err) => console.log('Error on test4:', err));