JavaScript编程设计模式之观察者模式(Observer Pattern)实例详解

function ObserverList(){ this.observerList = [];}ObserverList.prototype.Add = function( obj ){ return this.observerList.push( obj );};ObserverList.prototype.Empty = function(){ this.observerList = [];};ObserverList.prototype.Count = function(){ return this.observerList.length;};ObserverList.prototype.Get = function( index ){ if( index > -1 && index < this.observerList.length ){  return this.observerList[ index ]; }};ObserverList.prototype.Insert = function( obj, index ){ var pointer = -1; if( index === 0 ){  this.observerList.unshift( obj );  pointer = index; }else if( index === this.observerList.length ){  this.observerList.push( obj );  pointer = index; } return pointer;};ObserverList.prototype.IndexOf = function( obj, startIndex ){ var i = startIndex, pointer = -1; while( i < this.observerList.length ){  if( this.observerList[i] === obj ){   pointer = i;  }  i++; } return pointer;};ObserverList.prototype.RemoveAt = function( index ){ if( index === 0 ){  this.observerList.shift(); }else if( index === this.observerList.length -1 ){  this.observerList.pop(); }};// Extend an object with an extensionfunction extend( extension, obj ){ for ( var key in extension ){  obj[key] = extension[key]; }}

function Subject(){ this.observers = new ObserverList();}Subject.prototype.AddObserver = function( observer ){ this.observers.Add( observer );};Subject.prototype.RemoveObserver = function( observer ){ this.observers.RemoveAt( this.observers.IndexOf( observer, 0 ) );};Subject.prototype.Notify = function( context ){ var observerCount = this.observers.Count(); for(var i=0; i < observerCount; i++){  this.observers.Get(i).Update( context ); }};

// The Observerfunction Observer(){ this.Update = function(){  // ... };}

// A very simple new mail handler// A count of the number of messages receivedvar mailCounter = 0;// Initialize subscribers that will listen out for a topic// with the name "inbox/newMessage".// Render a preview of new messagesvar subscriber1 = subscribe( "inbox/newMessage", function( topic, data ) { // Log the topic for debugging purposes console.log( "A new message was received: ", topic ); // Use the data that was passed from our subject // to display a message preview to the user $( ".messageSender" ).html( data.sender ); $( ".messagePreview" ).html( data.body );});// Here's another subscriber using the same data to perform// a different task.// Update the counter displaying the number of new// messages received via the publishervar subscriber2 = subscribe( "inbox/newMessage", function( topic, data ) { $('.newMessageCounter').html( mailCounter++ );});publish( "inbox/newMessage", [{ sender:"hello@google.com", body: "Hey there! How are you doing today?"}]);// We could then at a later point unsubscribe our subscribers// from receiving any new topic notifications as follows:// unsubscribe( subscriber1, );// unsubscribe( subscriber2 );

// Publish// jQuery: $(obj).trigger("channel", [arg1, arg2, arg3]);$( el ).trigger( "/login", [{username:"test", userData:"test"}] );// Dojo: dojo.publish("channel", [arg1, arg2, arg3] );dojo.publish( "/login", [{username:"test", userData:"test"}] );// YUI: el.publish("channel", [arg1, arg2, arg3]);el.publish( "/login", {username:"test", userData:"test"} );// Subscribe// jQuery: $(obj).on( "channel", [data], fn );$( el ).on( "/login", function( event ){...} );// Dojo: dojo.subscribe( "channel", fn);var handle = dojo.subscribe( "/login", function(data){..} );// YUI: el.on("channel", handler);el.on( "/login", function( data ){...} );// Unsubscribe// jQuery: $(obj).off( "channel" );$( el ).off( "/login" );// Dojo: dojo.unsubscribe( handle );dojo.unsubscribe( handle );// YUI: el.detach("channel");el.detach( "/login" );

var pubsub = {};(function(q) {  var topics = {},    subUid = -1;  // Publish or broadcast events of interest  // with a specific topic name and arguments  // such as the data to pass along  q.publish = function( topic, args ) {    if ( !topics[topic] ) {      return false;    }    var subscribers = topics[topic],      len = subscribers ? subscribers.length : 0;    while (len--) {      subscribers[len].func( topic, args );    }    return this;  };  // Subscribe to events of interest  // with a specific topic name and a  // callback function, to be executed  // when the topic/event is observed  q.subscribe = function( topic, func ) {    if (!topics[topic]) {      topics[topic] = [];    }    var token = ( ++subUid ).toString();    topics[topic].push({      token: token,      func: func    });    return token;  };  // Unsubscribe from a specific  // topic, based on a tokenized reference  // to the subscription  q.unsubscribe = function( token ) {    for ( var m in topics ) {      if ( topics[m] ) {        for ( var i = 0, j = topics[m].length; i < j; i++ ) {          if ( topics[m][i].token === token) {            topics[m].splice( i, 1 );            return token;          }        }      }    }    return this;  };}( pubsub ));

// Another simple message handler// A simple message logger that logs any topics and data received through our// subscribervar messageLogger = function ( topics, data ) {  console.log( "Logging: " + topics + ": " + data );};// Subscribers listen for topics they have subscribed to and// invoke a callback function (e.g messageLogger) once a new// notification is broadcast on that topicvar subscription = pubsub.subscribe( "inbox/newMessage", messageLogger );// Publishers are in charge of publishing topics or notifications of// interest to the application. e.g:pubsub.publish( "inbox/newMessage", "hello world!" );// orpubsub.publish( "inbox/newMessage", ["test", "a", "b", "c"] );// orpubsub.publish( "inbox/newMessage", { sender: "hello@google.com", body: "Hey again!"});// We cab also unsubscribe if we no longer wish for our subscribers// to be notified// pubsub.unsubscribe( subscription );// Once unsubscribed, this for example won't result in our// messageLogger being executed as the subscriber is// no longer listeningpubsub.publish( "inbox/newMessage", "Hello! are you still there?" );