JavaScript设计模式-单例模式-守望者-AIR技术交流

破晓发表于 2016-8-3 12:12:52

JavaScript设计模式----单例模式

来源：http://div.io/topic/1792<div> </div><div><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">声明：这个系列为阅读《JavaScript设计模式与开发实践》 ----曾探@著一书的读书笔记<h3 style="font-size: 20px; counter-reset: subsection 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">1.单例模式的特点和定义</h3><blockquote style="margin: 32px 28px; padding-left: 14px; border-left-width: 3px; border-left-style: solid; border-left-color: rgb(204, 204, 204); line-height: 1.6; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px;">保证一个类仅有一个实例，并且提供一个访问它的全局访问点。</blockquote><h3 style="font-size: 20px; counter-reset: subsection 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">2.传统面向对象语言的单例模式</h3><h4 style="font-size: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">2.1传统语言描述的单例模式JavaScript实现</h4><pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">var Singleton = function(name) {
this.name = name;
this.instance = null;
};

Singleton.prototype.getName = function() {
alert(this.name);
};

Singleton.getInstance = function(name) {
if (!this.instance) {
 this.instance = new Singleton(name);
}

return this.instance;
};

var a = Singleton.getInstance('seven1');
var b = Singleton.getInstance('seven2');</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">或者使用闭包的形式创建单例模式,同时符合惰性单例的特性<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">var Singleton = function(name) {
this.name = name;
};

Singleton.prototype.getName = function() {
alert(this.name);
};

//利用闭包的特性创建单例,同时符合惰性单例的特性
Singleton.getInstance = (function(name) {
var instance;
return function(name){
 if (!instance) {
 instance = new Singleton(name);
 }
}
})();

var a = Singleton.getInstance('seven1');
var b = Singleton.getInstance('seven2');

console.log(a===b); //true</code></pre><h4 style="font-size: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">2.2透明的单例模式：</h4><pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">//反面的单例模式的例子

var CreateDiv = (function() {
var instance;
var CreateDiv = function(html) {
 if (instance) {
 return instance;
 }
 this.html = html;
 this.init();
 return instance = this;
};

CreateDiv.prototype.init = function() {
 var div = document.createElement('div');
 div.innerHTML = this.html;
 document.body.appendChild(div);
}

return CreateDiv;

})();

var a = new CreateDiv('seven1');
var b = new CreateDiv('seven2');</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">这样编写单例模式的缺点：<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">为了把<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">instance</code>封装起来，我们使用了自执行的匿名函数和闭包，并且让这个匿名函数返回真正的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">Singleton</code>构造方法，这增加了一些程序的复杂度。<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">CreateDiv</code>的构造函数负责了两件事情。1.创建对像和执行初始化<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">init</code>方法，第二是保证只有一个对象。不符合设计模式中的单一职责的概念。<h4 style="font-size: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">2.3引入代理实现单例模式</h4><pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">var CreateDiv = function(html) {
this.html = html;
this.init();
};

CreateDiv.prototype.init = function() {
var div = document.createElement('div');
div.innerHTML = this.html;
document.body.appendChild(div);
}

var ProxySingletonCreateDiv = (function() {
var instance;
return function(html) {
 if (!instance) {
 instance = new CreateDiv(html);
 }
 return instance;
}
})();

var a = new ProxySingletonCreateDiv('seven1');
var b = new ProxySingletonCreateDiv('seven2');</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">引入代理实现单例模式的特点：<p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">我们负责管理单例的逻辑移到了代理类<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">ProxySingletonCreateDiv</code>中。这样一来，<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">CreateDiv</code>就变成了一个普通的类，他跟<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">ProxySingletonCreateDiv</code>组合起来可以达到单例模式的效果。<h3 style="font-size: 20px; counter-reset: subsection 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">3.JavaScript的单例模式对比</h3><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">在以上的代码中实现的单例模式都混入了传统面向对象语言的特点。而没有利用JavaScript这们语言的特点来实现一个单例模式。<h4 style="font-size: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">3.1惰性单例的例子</h4><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">概念描述：<blockquote style="margin: 32px 28px; padding-left: 14px; border-left-width: 3px; border-left-style: solid; border-left-color: rgb(204, 204, 204); line-height: 1.6; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px;">惰性单例指的是在需要的时候才创建对象的实例。惰性单例是单例模式的重点。</blockquote><pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">var createLoginLayer=(function(){
var div;
return function(){
 if(!div){
 div=document.createElement('div');
 //创建一个登录框
 }
 return div;
}
})();

document.getElementById('loginBtn').onclick=function(){
var loginLayer=createLoginLayer();
loginLayer.style.display='block';
};</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">代码解析： 这里的对惰性单例的实现主要是只有单例了网页上的登录按钮，才会去创建，登录框的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">dom</code>节点，并且只是创建一次。<h4 style="font-size: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">3.2通用的单例模式例子</h4><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">根据3.1的代码示例，我们的单例对像，但是并不是通用的，比如我们要创建的不是<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">div</code>而是<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">iframe</code>，那要怎么办呢？<pre class="prettyprint lang-javascript prettyprinted" style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; padding: 6px 10px; border: 1px solid rgb(221, 221, 221); font-size: 12px; line-height: 18px; overflow: auto; border-radius: 3px; word-break: break-all; color: rgb(51, 51, 51); background-color: rgb(248, 248, 248);"><code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: 1.5; border: 0px none; border-radius: 0px; font-size: inherit; background: none;">//获取单例
var getSingle = function(fn){
var result;
return function (){
 return result || (result=fn.apply(this,arguments));
};
};

//创建div登录框
var createLoginLayer=function (){
var div= document.createElement('div');
div.innerHTML='我是登录框';
document.body.appendChild(div);
return div;
};

//创建iframe的dom节点
var createIframe=function(){
//创建irame节点的代码
}

var createSingleLoginLayer = getSingle(createLoginLayer);
var createSingleIframe=getSingle(createIframe);

var loginLayer1 = createSingleLoginLayer();
var loginLayer2 = createSingleLoginLayer();

var iframe1=createSingleIframe();
var iframe2=createSingleIframe();

console.log(loginLayer1 === loginLayer2);</code></pre><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">通用的单例创建的例子就是通过封装一个<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">getSingle</code>需要实现单例模式的对象。而且只是会只创建一次。因为使用了闭包的原因通过<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">getSingle</code>创建的<code style="font-family: consolas, monaco, menlo, "courier new", courier, monospace; display: inline-block; line-height: normal; margin-right: 0.25em; margin-left: 0.25em; padding-right: 0.4em; padding-left: 0.4em; border: 1px solid rgb(221, 221, 221); border-radius: 3px; background-color: rgb(248, 248, 248);">result</code>会在内存中一直存在不会销毁（除非页面关闭，或者手动释放）。<h3 style="font-size: 20px; counter-reset: subsection 0; font-weight: normal; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif;">总结：</h3><p style="margin-top: 18px; margin-bottom: 18px; color: rgb(51, 51, 51); font-family: "helvetica neue", tahoma, "hiragino sans gb", stheiti, "wenquanyi micro hei", 微软雅黑, 宋体, sans-serif; font-size: 16px; line-height: 27.2px;">单例模式是一种简单但非常实用的模式，特别是惰性单例技术，在合适的时候才创建对像，并且只创建唯一的一个。更奇妙的是，创建对象和管理单例的职责被分布在两个不同的方法中，这两个方法组合起来才具有单例模式的威力。</div>

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JavaScript设计模式----单例模式