Run special function pseudo synchronously using "yield" https://developer.mozilla.org/en-US/docs/JavaScript/New_in_JavaScript/1.7#Generators

async_yield.js

sync(f);

function sync(f) {
	var g = f.__generator = f();
	g.next();
}
function f() {
	var res;
	_log("Start first async...");
	setTimeout(function() {
		res = 1;
		f.__generator.next();
	}, 2000);
	yield;
	_log("First async done: " + res + "\nStart second async...");
	setTimeout(function() {
		++res;
		f.__generator.next();
	}, 2000);
	yield;
	_log("Second async done: " + res);
	yield;
}
function _log(s) {
	s = "[yield] " + ts() + " " + s;
	if("Services" in window && "console" in Services)
		Services.console.logStringMessage(s);
	else if("console" in window && "log" in console)
		console.log(s);
	else
		setTimeout(function() { throw new Error(s); }, 0);
}
function ts() {
	var d = new Date();
	var ms = d.getMilliseconds();
	return d.toLocaleFormat("%M:%S:") + "000".substr(String(ms).length) + ms;
}

async_yield_lock.js

trySync(f, 0);
trySync(f, 1);
trySync(f, 2);

function trySync(f, i) {
	if(sync(f))
		_log("Ok: " + i);
	else
		_log("Fail: " + i);
}
function sync(f) {
	if("__inProgress" in f) {
		_log("Previous operation aren't finished, exit!");
		return false;
	}
	f.__inProgress = true;
	var g = f.__generator = f();
	g.next();
	return true;
}
function cleanup(f) {
	delete f.__inProgress;
	delete f.__generator;
	_log("Cleanup generator");
}
function f() {
	var res;
	_log("Start first async...");
	setTimeout(function() {
		res = 1;
		f.__generator.next();
	}, 1000);
	yield;
	_log("First async done: " + res + "\nStart second async...");
	setTimeout(function() {
		++res;
		f.__generator.next();
	}, 1000);
	yield;
	_log("Second async done: " + res);
	cleanup(f);
	yield;
}
function _log(s) {
	s = "[yield] " + ts() + " " + s;
	if("Services" in window && "console" in Services)
		Services.console.logStringMessage(s);
	else if("console" in window && "log" in console)
		console.log(s);
	else
		setTimeout(function() { throw new Error(s); }, 0);
}
function ts() {
	var d = new Date();
	var ms = d.getMilliseconds();
	return d.toLocaleFormat("%M:%S:") + "000".substr(String(ms).length) + ms;
}

async_yield_parallel.js

sync(f, 0);
sync(f, 1);
sync(f, 2);

function sync(f/*, arg1, */) {
	// Array.slice() is the same as Array.prototype.slice.call(), Firefox only
	var g = f.__generator = f.apply(this, Array.slice(arguments, 1));
	g.next();
}
function f(n) {
	var g = f.__generator;
	delete f.__generator;
	var res;
	_log("Start first async... #" + n);
	setTimeout(function() {
		res = 1;
		g.next();
	}, 1000);
	yield;
	_log("First async done: " + res + "\nStart second async... #" + n);
	setTimeout(function() {
		++res;
		g.next();
	}, 1000);
	yield;
	_log("Second async done: " + res + " #" + n);
	yield;
}
function _log(s) {
	s = "[yield] " + ts() + " " + s;
	if("Services" in window && "console" in Services)
		Services.console.logStringMessage(s);
	else if("console" in window && "log" in console)
		console.log(s);
	else
		setTimeout(function() { throw new Error(s); }, 0);
}
function ts() {
	var d = new Date();
	var ms = d.getMilliseconds();
	return d.toLocaleFormat("%M:%S:") + "000".substr(String(ms).length) + ms;
}

async_yield_queue.js

sync(f);
sync(f);
sync(f);

function sync(f) {
	if("__inProgress" in f) {
		if(!("__pending" in f))
			f.__pending = [];
		var i = f.__pending.push(
			function() {
				delete f.__pending[i];
				sync(f);
			}
		) - 1;
		_log("Pending: " + i);
		return;
	}
	f.__inProgress = true;
	var g = f.__generator = f();
	g.next();
}
function next(f) {
	delete f.__inProgress;
	delete f.__generator;
	if("__pending" in f) for(var i in f.__pending) if(f.__pending.hasOwnProperty(i)) {
		_log("Run pending: " + i);
		f.__pending[i]();
		return;
	}
	delete f.__pending;
	_log("Destroy pendings");
}
function f() {
	var res;
	_log("Start first async...");
	setTimeout(function() {
		res = 1;
		f.__generator.next();
	}, 1000);
	yield;
	_log("First async done: " + res + "\nStart second async...");
	setTimeout(function() {
		++res;
		f.__generator.next();
	}, 1000);
	yield;
	_log("Second async done: " + res);
	next(f);
	yield;
}
function _log(s) {
	s = "[yield] " + ts() + " " + s;
	if("Services" in window && "console" in Services)
		Services.console.logStringMessage(s);
	else if("console" in window && "log" in console)
		console.log(s);
	else
		setTimeout(function() { throw new Error(s); }, 0);
}
function ts() {
	var d = new Date();
	var ms = d.getMilliseconds();
	return d.toLocaleFormat("%M:%S:") + "000".substr(String(ms).length) + ms;
}