中间人模式

The mediator pattern usually implements a single object that becomes a shared resource through all of the different pieces of an application. 它通常用于更高层级，用于协调各个部件之间的通信。

优点

• 减少了多到多和多到一个之间的通信
• 帮助我们减少依赖
• 帮助我们减少耦合

缺点

• 引入了单点入口问题
• 可能会使程序看起来笨重，对性能也有影响

var Mediator = ( function( window, undefined ) {

    function Mediator() {
        this._topics = {};
    }

    Mediator.prototype.subscribe = function mediatorSubscribe( topic, callback ) {
        if( ! this._topics.hasOwnProperty( topic ) ) {
            this._topics[ topic ] = [];
        }

        this._topics[ topic ].push( callback );
        return true;
    };

    Mediator.prototype.unsubscribe = function mediatorUnsubscrive( topic, callback ) {
        if( ! this._topics.hasOwnProperty( topic ) ) {
            return false;
        }

        for( var i = 0, len = this._topics[ topic ].length; i < len; i++ ) {
            if( this._topics[ topic ][ i ] === callback ) {
                this._topics[ topic ].splice( i, 1 );
                return true;
            }
        }

        return false;
    };

    Mediator.prototype.publish = function mediatorPublish() {
        var args = Array.prototype.slice.call( arguments );
        var topic = args.shift();

        if( ! this._topics.hasOwnProperty( topic ) ) {
            return false;
        }

        for( var i = 0, len = this._topics[ topic ].length; i < len; i++ ) {
            this._topics[ topic ][ i ].apply( undefined, args );
        }
        return true;
    };

    return Mediator;

} )( window );

// example subscriber function
var Subscriber = function ExampleSubscriber( myVariable ) {
  console.log( myVariable );
};

// example usages
var myMediator = new Mediator();
myMediator.subscribe( 'some event', Subscriber );
myMediator.publish( 'some event', 'foo bar' ); // console logs "foo bar"