开源微信小程序商城_JavaScript编程设计模式之观察

阅读  ·  发布日期 2021-01-11 13:30  ·  admin
JavaScript编程设计模式之观察者模式(Observer Pattern)实例详解       这篇文章主要介绍了JavaScript编程设计模式之观察者模式(Observer Pattern),简单说明了观察者模式的概念、原理并结合实例形式详细给出了观察者模式的相关实现与使用技巧,需要的朋友可以参考下

本文实例讲述了JavaScript编程设计模式之观察者模式。分享给大家供大家参考,具体如下:

简介

简单的解释观察者模式,就是一个对象(subject)维护一个依赖他的对象(observers)列表,当自身状态发生变化时,自动通知所有观察者对象。当某个对象不需要获得通知时,可以从对象列表中删除掉。

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 extension
function extend( extension, obj ){
 for ( var key in extension ){
 obj[key] = extension[key];

Subject拥有增加和删除Observer的能力

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 );

最后定义一个观察者对象,实现update方法

// The Observer
function Observer(){
 this.Update = function(){
 // ...

当有多个观察者,只需扩展上面的基本对象,并重写Update方法。

尽管观察则模式被广泛使用,但在JS中经常使用它的变体: 发布订阅模式

发布订阅模式通过一个topic/event通道,解耦了观察者模式中Subject(发布者)和Observer(订阅者)之间耦合的问题,在JS中被广泛使用。

下面简单的例子说明了使用发布订阅模式的基本结构

// A very simple new mail handler
// A count of the number of messages received
var mailCounter = 0;
// Initialize subscribers that will listen out for a topic
// with the name "inbox/newMessage".
// Render a preview of new messages
var 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
 $( ".( data.sender );
 $( ".( 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 publisher
var subscriber2 = subscribe( "inbox/newMessage", function( topic, data ) {
 $('.( mailCounter++ );
publish( "inbox/newMessage", [{
 sender:"hello",
 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 );

发布订阅模式的实现

许多Js库都很好的实现了发布订阅模式,例如Jquery的自定义事件功能。

// 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" );

简单实现

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 i++ ) {
 if ( topics[m][i].token === token) {
 topics[m].splice( i, 1 );
 return token;
 return this;
}( pubsub ));

使用方法

// Another simple message handler
// A simple message logger that logs any topics and data received through our
// subscriber
var 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 topic
var 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!" );
// or
pubsub.publish( "inbox/newMessage", ["test", "a", "b", "c"] );
// or
pubsub.publish( "inbox/newMessage", {
 sender: "hello",
 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 listening
pubsub.publish( "inbox/newMessage", "Hello! are you still there " );

更多关于JavaScript相关内容可查看本站专题:《》、《》、《》、《》、《》、《》及《》

希望本文所述对大家JavaScript程序设计有所帮助。