Mediator mode of javascript design pattern Mediator_javascript skills

var Participant = function(name) {
    this.name = name;
    this.chatroom = null;
};
Participant.prototype = {
    send: function(message, to) {
        this.chatroom.send(message, this, to);
    },
    receive: function(message, from) {
        log.add(from.name " to " this.name ": " message);
    }
};
var Chatroom = function() {
    var participants = {};
    return {
        register: function(participant) {
            participants[participant.name] = participant;
            participant.chatroom = this;
        },
        send: function(message, from, to) {
            if (to) {                  
                to.receive(message, from);   
            } else {                    
                for (key in participants) {  
                    if (participants[key] !== from) {
                        participants[key].receive(message, from);
                    }
                }
            }
        }
    };
};
var log = (function() {
    var log = "";
    return {
        add: function(msg) { log = msg "n"; },
        show: function() { alert(log); log = ""; }
    }
})();
function run() {
    var yoko = new Participant("Yoko");
    var john = new Participant("John");
    var paul = new Participant("Paul");
    var ringo = new Participant("Ringo");
    var chatroom = new Chatroom();
    chatroom.register(yoko);
    chatroom.register(john);
    chatroom.register(paul);
    chatroom.register(ringo);
    yoko.send("All you need is love.");
    yoko.send("I love you John.");
    john.send("Hey, no need to broadcast", yoko);
    paul.send("Ha, I heard that!");
    ringo.send("Paul, what do you think?", paul);
    log.show();
}

function Player(name) {
    this.points = 0;
    this.name = name;
}
Player.prototype.play = function () {
    this.points = 1;
    mediator.played();
};
var scoreboard = {
    element:document.getElementById('results'),
    update:function (score) {
        var i, msg = '';
        for (i in score) {
            if (score.hasOwnProperty(i)) {
                msg = '

' i ': ';
                msg = score[i];
                msg = '

';
            }
        }
        this.element.innerHTML = msg;
    }
};
var mediator = {
    players:{},
    setup:function () {
        var players = this.players;
        players.home = new Player('Home');
        players.guest = new Player('Guest');
    },
    played:function () {
        var players = this.players,
                score = {
                    Home:players.home.points,
                    Guest:players.guest.points
                };
        scoreboard.update(score);
    },
    keypress:function (e) {
        e = e || window.event;
        if (e.which === 49) {
            mediator.players.home.play();
            return;
        }
        if (e.which === 48) {
            mediator.players.guest.play();
            return;
        }
    }
};
mediator.setup();
window.onkeypress = mediator.keypress;
setTimeout(function () {
    window.onkeypress = null;
    console.log('Game over!');
}, 30000);

四，总结一下

Why Mediator ?

各个对象之间的交互操作非常多，每个对象的行为操作都依赖彼此对方，修改一个对象的行为，同时会涉及到修改很多其他对象的行为，

如果使用Mediator模式，可以使各个对象间的耦合松散,只需关心和 Mediator的关系,使多对多的关系变成了一对多的关系，

可以降低系统的复杂性，提高可修改扩展性。

使用中介者模式的场合

1.一组定义良好的对象，现在要进行复杂的通信。

2.定制一个分布在多个类中的行为，而又不想生成太多的子类。

可以看出，中介对象主要是用来封装行为的，行为的参与者就是那些对象，但是通过中介者，这些对象不用相互知道。（迪米特法则的具体实现）

使用中介者模式的优点：

1.降低了系统对象之间的耦合性，使得对象易于独立的被复用。

2.提高系统的灵活性，使得系统易于扩展和维护。

使用中介者模式的缺点：

中介者模式的缺点是显而易见的，因为这个“中介“承担了较多的责任，所以一旦这个中介对象出现了问题，那么整个系统就会受到重大的影响。