bjouhier/asyncgen.js

## asyncgen.js
(function() {
	var GENERATOR_PROTO = Object.getPrototypeOf((function() {
		yield;
	})());

	function isGenerator(val) {
		return typeof val === 'object' && Object.getPrototypeOf(val) === GENERATOR_PROTO;
	}

	var PENDING = {};

	window.AsyncGen = {
		run: function(fn, args, idx) {
			var cb = args[idx],
				g;

			function resume(err, val) {
				while (g) {
					try {
						val = err ? g.throw(err) : g.send(val);
						err = null;
						// if we get PENDING, the current call completed with a pending I/O
						// resume will be called again when the I/O completes. So just return here.
						if (val === PENDING) return;
						// if we get [PENDING, e, r], the current call invoked its callback synchronously
						// we just loop to send/throw what the callback gave us.
						if (val && val[0] === PENDING) {
							err = val[1];
							val = val[2];
						}
						// else, if g yielded a value which is not a generator, g is done.
						// so we unwind it we send val to the parent generator (or through cb if we are at the top)
						else if (!isGenerator(val)) {
							g.close();
							g = g.prev;
						}
						// else, we got a new generator which means that g called another generator function
						// the new generator become current and we loop with g.send(undefined) (equiv to g.next())
						else {
							val.prev = g;
							g = val;
							val = undefined;
						}
					} catch (ex) {
						// the send/throw call failed.
						// we unwind the current generator and we rethrow into the parent generator (or through cb if at the top)
						g.close();
						g = g.prev;
						err = ex;
						val = undefined;
					}
				}
				// we have exhausted the stack of generators.
				// return the result or error through the callback.
				cb(err, val);
			}
			// set resume as the new callback
			args[idx] = resume;
			// call fn to get the initial generator
			g = fn.apply(this, args);
			// start the resume loop
			resume();
		},
		invoke: function(that, fn, args, idx) {
			// Set things up so that call returns:
			// * PENDING if it completes with a pending I/O (and cb will be called later)
			// * [PENDING, e, r] if the callback is called synchronously.
			var result = PENDING,
				sync = true;
			var cb = args[idx];
			args[idx] = function(e, r) {
				if (sync) {
					result = [PENDING, e, r];
				} else {
					cb(e, r);
				}
			}
			fn.apply(that, args);
			sync = false;
			return result;
		}
	};
})();

## hello.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
                    "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <script src="asyncgen.js" type="application/javascript;version=1.7"></script>
  <script src="hello.js" type="application/javascript;version=1.7"></script>
</head>
<body>
  <h1>Asynchronous hello world with generators (Firefox only)</h1>
  <button onClick="javascript:startDemo();return;">Start</button>
  <div id="output"></div>
</body>
</html>


## hello.js

function print(str) {
	document.getElementById('output').innerHTML += "<p>" + str + "</p>";
}

function delay(_, result) {
  yield AsyncGen.invoke(this, setTimeout, [_, 1000], 0);
  yield result;
}

function helloWorld(_) {
  print("starting ...");
  print(yield delay(_, 'hello ...'));
  print(yield delay(_, '... world'));
  print("done!");
  yield;
}

function startDemo() {
	AsyncGen.run(helloWorld, [function(err) {
	  if (err) alert(err);
	  else print("continuing with callback");
	}], 0);
}
	(function() {
	var GENERATOR_PROTO = Object.getPrototypeOf((function() {
	yield;
	})());

	function isGenerator(val) {
	return typeof val === 'object' && Object.getPrototypeOf(val) === GENERATOR_PROTO;
	}

	var PENDING = {};

	window.AsyncGen = {
	run: function(fn, args, idx) {
	var cb = args[idx],
	g;

	function resume(err, val) {
	while (g) {
	try {
	val = err ? g.throw(err) : g.send(val);
	err = null;
	// if we get PENDING, the current call completed with a pending I/O
	// resume will be called again when the I/O completes. So just return here.
	if (val === PENDING) return;
	// if we get [PENDING, e, r], the current call invoked its callback synchronously
	// we just loop to send/throw what the callback gave us.
	if (val && val[0] === PENDING) {
	err = val[1];
	val = val[2];
	}
	// else, if g yielded a value which is not a generator, g is done.
	// so we unwind it we send val to the parent generator (or through cb if we are at the top)
	else if (!isGenerator(val)) {
	g.close();
	g = g.prev;
	}
	// else, we got a new generator which means that g called another generator function
	// the new generator become current and we loop with g.send(undefined) (equiv to g.next())
	else {
	val.prev = g;
	g = val;
	val = undefined;
	}
	} catch (ex) {
	// the send/throw call failed.
	// we unwind the current generator and we rethrow into the parent generator (or through cb if at the top)
	g.close();
	g = g.prev;
	err = ex;
	val = undefined;
	}
	}
	// we have exhausted the stack of generators.
	// return the result or error through the callback.
	cb(err, val);
	}
	// set resume as the new callback
	args[idx] = resume;
	// call fn to get the initial generator
	g = fn.apply(this, args);
	// start the resume loop
	resume();
	},
	invoke: function(that, fn, args, idx) {
	// Set things up so that call returns:
	// * PENDING if it completes with a pending I/O (and cb will be called later)
	// * [PENDING, e, r] if the callback is called synchronously.
	var result = PENDING,
	sync = true;
	var cb = args[idx];
	args[idx] = function(e, r) {
	if (sync) {
	result = [PENDING, e, r];
	} else {
	cb(e, r);
	}
	}
	fn.apply(that, args);
	sync = false;
	return result;
	}
	};
	})();
	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
	"http://www.w3.org/TR/html4/loose.dtd">
	<html>
	<head>
	<script src="asyncgen.js" type="application/javascript;version=1.7"></script>
	<script src="hello.js" type="application/javascript;version=1.7"></script>
	</head>
	<body>
	<h1>Asynchronous hello world with generators (Firefox only)</h1>
	<button onClick="javascript:startDemo();return;">Start</button>
	<div id="output"></div>
	</body>
	</html>

	function print(str) {
	document.getElementById('output').innerHTML += "<p>" + str + "</p>";
	}

	function delay(_, result) {
	yield AsyncGen.invoke(this, setTimeout, [_, 1000], 0);
	yield result;
	}

	function helloWorld(_) {
	print("starting ...");
	print(yield delay(_, 'hello ...'));
	print(yield delay(_, '... world'));
	print("done!");
	yield;
	}

	function startDemo() {
	AsyncGen.run(helloWorld, [function(err) {
	if (err) alert(err);
	else print("continuing with callback");
	}], 0);
	}