javascript设计模式之观察者模式

观察者模式又称发布/订阅模式   publish/subscribe

　　它是一种一对多的关系，让多个观察者对象同时监听某一主题对象，这个主题对象的状态发生变化时就会通知所有的观察者对象，使得他们能够自动更新自己。

 function msgBus(){

     var msgMap = {}; // internal message bus
     var instance = {};

     /**
      * @function subscribe
      * @description subscribe message listener.
      * @param msgType {string} - message type to be listen.
      * @param handler {function} - handler function when the message sent.
      * @instance
      */
     instance.subscribe = function(msgType,handler){
         if(msgType == null){
             console.error("Message type is null");
             return instance;
         }
         if(handler == null){
             console.error("handler is null");
             return instance;
         }
         var subscribeArray = msgMap[msgType];
         if(subscribeArray == null){
             subscribeArray = new Array();
             msgMap[msgType] = subscribeArray;
         }
         if(subscribeArray.indexOf(handler) < 0){
             subscribeArray.push(handler);
         }
         return instance;
     }

     /**
      * @function unsubscribe
      * @description unsubscribe message listener.
      * @param msgType {string} - message type to be unsubscribe.
      * @param handler {function} - handler function to be removed.
      * @instance
      */

     instance.unsubscribe = function(msgType,handler){
         var subscribeArray = msgMap[msgType];
         if(subscribeArray != null){
             var index = subscribeArray.indexOf(handler);
             if(index > 0){
                 subscribeArray.splice(index,1);
             }
         }

         return instance;
     }

     /**
      * @function publish
      * @description publish message.
      * @param msgType {string} - message type to be published.
      * @param data {object} - message data.
      * @instance
      */
     instance.publish = function(msgType,data){
         var subscribeArray = msgMap[msgType];
         if(subscribeArray == null){
             return;
         }
         for(var i=0;i<subscribeArray.length;i++){
             try{
                 subscribeArray[i](data);
             }catch(e){
                 console.error("Error when sending Message: "+msgType);
             }
         }

         return instance;
     }

     return instance;
 }

测试一下：

var instance = msgBus();
instance.subscribe("subscribe",function(data){console.log("this is "+data)});

instance.publish("subscribe","cangjingkong"); // this is cangjingkong