Simulate C# async/await in ES6 thanks to generators

asyncAwaitEnabler.js

//	http://deploytonenyures.blogspot.fr/2015/06/simulating-await-with-es6-generators.html

//as of node 0.12.4 we still need the -harmony flag to enable generators

var print = console.log;

//---------------------
// class used to represent an asynchronous operation
//it's a sort of "poor man's" Promise 

//first parameter is an async function func, the remaining parameters are the normal params
//then a callback will be provided later on by setting the nextStep property
//func will call nextStep once finished passing over its result
function TaskInfo(){
	this.arguments = [].slice.call(arguments, 0);
	this.func =  this.arguments.shift();
	this.nextStep = null;
}

TaskInfo.prototype.run = function(){
	//duplicate it
	var args = this.arguments.slice();
	args.push(this.nextStep);
	this.func.apply(this, args);
};
//---------------------

//receives a generator function that returns a TaskInfo on each "iteration"
//this function implements the asynchronous loop that will keep calling the generator object
function awaitEnableAndRun(generatorFunc, endCallback){
	var loop = function(returnValue){
		//notice that the first call to next is supposed to crash if it receives a parameter, 
		//but it's not the case as of this writing neither in node or firefox. If it were so, I would have to adapt this a bit
		var res = generator.next(returnValue);
		if (!res.done){
			var taskInfo = res.value;
			taskInfo.nextStep = loop;
			taskInfo.run();
		}
		else{
			endCallback();
		}
	};
	var generator = generatorFunc();
	loop();
}

//---------------------

//sample of asynchronous function
function getFileAsync(fileId, onFinishedCallback){
	print("file retrieval " + fileId + " started");
	setTimeout(function(){
		print("file retrieval finished");
		//result of the async operation
		var file = {
			id : fileId,
			content: null
		};
		onFinishedCallback(file);
	}, 4000);
}

//using yield and TaskInfo to simulate c#'s await
function* getFiles(/*onFinished*/){
	print("getFiles started");
	//equivalent to a C# await call:
	//return a function 
	var file = yield (new TaskInfo(getFileAsync, "111")); 
	print("operating with file1: " + file.id);
	
	//equivalent to a C# await call:
	file = yield (new TaskInfo(getFileAsync, "222"));
	print("operating with file2" + file.id);
	
	//onFinished();
};


//let's go
print ("application started")
awaitEnableAndRun(getFiles, function(){
	print("application finished");
});