Extemely minimalistic implementation of promises/futures

chain.js

function chain(callback) {

	var queue = [];

	function _next() {
		var cb = queue.shift();
		if (cb) {
			cb(_next);
		}
	}

	setTimeout(_next, 0);

	var then = function(cb) {
		queue.push(cb);
		return { then: then }
	}

	return then(callback);
}

chain.min.js

//137 bytes
function chain(a){function c(){var a=b.shift();a&&a(c)}var b=[];setTimeout(c,0);var d=function(a){return b.push(a),{then:d}};return d(a)}

example.js

chain(function(next) {
	console.log('1');
	setTimeout(function() {
		console.log('2');
		next();
	}, 1000);
}).then(function(next) {
	console.log('3');
	setTimeout(function() {
		console.log('4');
		next();
	}, 1000);
}).then(function(next) {
	console.log('5');
	next();
});