Question

我正在尝试理解Observable / Observer设计模式。

这是我到目前为止的代码（来自Javascript Patterns的代码）：

            var publisher = {
            subscribers: {
                any: [] // event type: subscribers
            },
            publications: {
                any: []
            },
            subscribe: function (fn, type) {
                type = type || 'any';
                if (typeof this.subscribers[type] === "undefined") {
                    this.subscribers[type] = [];
                }

                this.subscribers[type].push(fn);

                if(typeof this.publications[type] === "undefined"){
                    return;
                }

                var pubs = this.publications[type],
                i,
                max = pubs.length

                for(i = 0;i<max;i++){
                    this.subscribers[type][i](pubs[i]);
                }

            },
            unsubscribe: function (fn, type) {
                this.visitSubscribers('unsubscribe', fn, type);
            },
            publish: function (publication, type) {
                var pubtype = type || 'any';
                this.visitSubscribers('publish', publication, type);
                if(typeof this.publications[pubtype] === "undefined") {
                    this.publications[pubtype] = [];
                }
                this.publications[pubtype].push(publication);
            },
            visitSubscribers: function (action, arg, type) {
                var pubtype = type || 'any',
                subscribers = this.subscribers[pubtype],
                i,
                max;

                if(typeof subscribers === 'undefined') {
                    return;
                }

                max = subscribers.length;

                for (i = 0; i < max; i += 1) {
                    if (action === 'publish') {
                        subscribers[i](arg);
                    } else {
                        if (subscribers[i] === arg) {
                            subscribers.splice(i, 1);
                        }
                    }
                }
            }
        };

        function makePublisher(o) {
            var i;
            for (i in publisher) {
                if (publisher.hasOwnProperty(i) && typeof publisher[i] === "function") {
                    o[i] = publisher[i];
                }
            }
            o.subscribers = {any: []};
            o.publications = {any: []};
        }

        var paper = {
            daily: function () {
                this.publish("big news today");
            },
            monthly: function () {
                this.publish("interesting analysis", "monthly");
            },
            yearly: function () {
                this.publish("every year","yearly");
            }
        };

        makePublisher(paper);

        var joe = {
            drinkCoffee: function (paper) {
                console.log('Just read ' + paper);
            },
            sundayPreNap: function (monthly) {
                console.log('About to fall asleep reading this ' + monthly);
            },
            onHolidays: function(yearly) {
                console.log('Holidays!'+yearly);
            }
        };


        paper.daily();
        paper.monthly();
        paper.yearly();

        paper.subscribe(joe.drinkCoffee);
        paper.subscribe(joe.onHolidays,'yearly');
        paper.subscribe(joe.sundayPreNap, 'monthly');

我想知道是否有可能允许客户端接收通知即使他们在之后注册了这些通知，也是。

我应该修改publisher.subscribe并检查是否未定义，是否发布事件类型？

提前致谢。

* 编辑1 *

我添加了一个publication对象来保存发布功能中的出版物。我还检查是否有发布类型的订阅者，如果没有，我会调用return。现在我需要弄清楚如何在订阅时通知他们旧版本。

* 编辑2 *

添加了新版本的工作脚本。它被认为是正确的还是最好的方法呢？

Answer 1

如果您希望订阅者在发送后收到通知，您只需要

对于每种不同的发布类型，请保留您为其获取的所有通知的列表。（发布时，将publication添加到相应的列表中）
更改订阅功能，以便它还将所有相应的存储通知发送给迟到的订阅者。

2.1也许你还应该创建一个单独的send_notification_to(arg, type, subscriber)方法，以避免代码重复visitSubscribers

发布后发布/订阅通知

1 个答案: