异步调用框架Async.Operation

Async = {
    Operation: function() {
        var callbackQueue = [];
        this.result = undefined;
        this.state = "running";
        this.completed = false;

        this.yield = function(result) {
            var self = this;
            setTimeout(function() {
                self.result = result;
                self.state = "completed";
                self.completed = true;

                while (callbackQueue.length > 0) {
                    var callback = callbackQueue.shift();
                    callback(self.result);
                }
            }, 1);
            return this;
        };

        this.addCallback = function(callback) {
            callbackQueue.push(callback);
            if (this.completed) {
                this.yield(this.result);
            }
            return this;
        };
    }
};