How to write in sync with ES6 (with generator & yield explanation). Thanks to Mr.Lucioato, author of waitfor-ES6 (https://github.com/luciotato/waitfor-ES6)

sync.js

"use strict";
const sync = function(fnGenerator) { 

	var args = Array.prototype.slice.call(arguments, 1);
	/**/ console.log('sync args', args.length, args)

	const callAsync = (funcAndArgs, callback) => {
		const argsOnly = Array.prototype.slice.call(funcAndArgs, 1);
		argsOnly.push(callback);
		/**/ console.log('callAsync', argsOnly)
		funcAndArgs[0].apply(null, argsOnly);
	}

	const iterator =  fnGenerator.apply(null, args);
	iterator.myCallback = (err, data) => {
		/**/ console.log('\nmyCallback', err, data)
		if (err) return iterator.throw(err);
		
		/**/ console.log('calling next')
		const nextPart = iterator.next(data);
		/**/ console.log('nextPart', nextPart)
		
		if (!nextPart.done) 
			return callAsync(nextPart.value, iterator.myCallback);
	};
	iterator.myCallback();
	
	return iterator;
}

const demoCallback = (v1, v2, callback) => {
	console.log('demoCallback');
	setTimeout( () => {
		console.log('demoCallback v1', v1, 'v2', v2);
		return callback(null, 'demoCallback done');
	}, 1e3)
}

function* demoGenerator() {
	/**/ console.log('demoGenerator');
	var args = Array.prototype.slice.call(arguments, 0);
	/**/ console.log('demoGenerator args', args.length, args)

	const data1 = yield [demoCallback, 1, 2];
	console.log('data1', data1);

	const data2 = yield [demoCallback, 3, 4];
	console.log('data2', data2);
}

sync(demoGenerator, 'a', 'b', 'c')