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- <h1 id="匿名函数和闭包">匿名函数和闭包</h1>
- <h4 id="在计算机科学中,闭包是函数的非局部变量(自由变量)的引用环境。">在计算机科学中,闭包是函数的非局部变量(自由变量)的引用环境。</h4>
- <blockquote>
- <p>包含自由变量的函数与为所有这些自由变量提供了变量绑定的环境一起,被称为闭包。</p>
- <p>以下内容为学习笔记,来自李炎恢老师的课堂纪要。</p>
- </blockquote>
- <h1 id="1匿名函数">1.匿名函数</h1>
- <blockquote>
- <h3 id="普通函数">普通函数</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//函数名是box</span>
- <span class="hljs-keyword">return</span> <span class="hljs-string">'Lee'</span>;
- }
- </code></pre>
- <h3 id="匿名函数">匿名函数</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//匿名函数,会报错</span>
- <span class="hljs-keyword">return</span> <span class="hljs-string">'Lee'</span>;
- }
- </code></pre>
- <h3 id="通过表达式自我执行">通过表达式自我执行</h3>
- <pre><code class="lang-js">(<span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//封装成表达式</span>
- alert(<span class="hljs-string">'Lee'</span>);
- })(); <span class="hljs-comment">//()表示执行函数,并且传参</span>
- </code></pre>
- <h3 id="把匿名函数赋值给变量">把匿名函数赋值给变量</h3>
- <pre><code class="lang-js"><span class="hljs-keyword">var</span> box = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//将匿名函数赋给变量</span>
- <span class="hljs-keyword">return</span> <span class="hljs-string">'Lee'</span>;
- };
- alert(box()); <span class="hljs-comment">//调用方式和函数调用相似</span>
- </code></pre>
- <h3 id="函数里的匿名函数">函数里的匿名函数</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//函数里的匿名函数,产生闭包</span>
- <span class="hljs-keyword">return</span> <span class="hljs-string">'Lee'</span>;
- }
- }
- alert(box()()); <span class="hljs-comment">//调用匿名函数</span>
- </code></pre>
- </blockquote>
- <h1 id="2闭包">2.闭包</h1>
- <blockquote>
- <p>闭包是指有权访问另一个函数作用域中的变量的函数,创建闭包的常见的方式,就是在
- 一个函数内部创建另一个函数,通过另一个函数访问这个函数的局部变量。</p>
- <h3 id="通过闭包可以返回局部变量">通过闭包可以返回局部变量</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> user = <span class="hljs-string">'Lee'</span>;
- <span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//通过匿名函数返回box()局部变量</span>
- <span class="hljs-keyword">return</span> user;
- };
- }
- alert(box()()); <span class="hljs-comment">//通过box()()来直接调用匿名函数返回值</span>
- <span class="hljs-keyword">var</span> b = box();
- alert(b()); <span class="hljs-comment">//另一种调用匿名函数返回值</span>
- </code></pre>
- <p>使用闭包有一个优点,也是它的缺点:就是可以把局部变量驻留在内存中,可以避免使
- 用全局变量。(全局变量污染导致应用程序不可预测性,每个模块都可调用必将引来灾难,
- 所以推荐使用私有的,封装的局部变量)。</p>
- <h3 id="通过全局变量来累加">通过全局变量来累加</h3>
- <pre><code class="lang-js"><span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>; <span class="hljs-comment">//全局变量</span>
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- age ++; <span class="hljs-comment">//模块级可以调用全局变量,进行累加</span>
- }
- box(); <span class="hljs-comment">//执行函数,累加了</span>
- alert(age); <span class="hljs-comment">//输出全局变量</span>
- <span class="hljs-comment">//通过局部变量无法实现累加</span>
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>;
- age ++; <span class="hljs-comment">//累加</span>
- <span class="hljs-keyword">return</span> age;
- }
- alert(box()); <span class="hljs-comment">//101</span>
- alert(box()); <span class="hljs-comment">//101,无法实现,因为又被初始化了</span>
- </code></pre>
- <h3 id="通过闭包可以实现局部变量的累加">通过闭包可以实现局部变量的累加</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>;
- <span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- age ++;
- <span class="hljs-keyword">return</span> age;
- }
- }
- <span class="hljs-keyword">var</span> b = box(); <span class="hljs-comment">//获得函数</span>
- alert(b()); <span class="hljs-comment">//调用匿名函数</span>
- alert(b()); <span class="hljs-comment">//第二次调用匿名函数,实现累加</span>
- </code></pre>
- <h3 id="循环里包含匿名函数">循环里包含匿名函数</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> arr = [];
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++) {
- arr[i] = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> i;
- };
- }
- <span class="hljs-keyword">return</span> arr;
- }
- <span class="hljs-keyword">var</span> b = box(); <span class="hljs-comment">//得到函数数组</span>
- alert(b.length); <span class="hljs-comment">//得到函数集合长度</span>
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < b.length; i++) {
- alert(b[i]()); <span class="hljs-comment">//输出每个函数的值,都是最后一个值</span>
- }
- </code></pre>
- <p>上面的例子输出的结果都是5,也就是循环后得到的最大的i 值。因为b[i]调用的是匿
- 名函数,匿名函数并没有自我执行,等到调用的时候,box()已执行完毕,i 早已变成5,所
- 以最终的结果就是5 个5。</p>
- <h3 id="循环里包含匿名函数-改1,自我执行匿名函数">循环里包含匿名函数-改1,自我执行匿名函数</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> arr = [];
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++) {
- arr[i] = (<span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">num</span>) </span>{ <span class="hljs-comment">//自我执行</span>
- <span class="hljs-keyword">return</span> num;
- })(i); <span class="hljs-comment">//并且传参</span>
- }
- <span class="hljs-keyword">return</span> arr;
- }
- <span class="hljs-keyword">var</span> b = box();
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < b.length; i++) {
- alert(b[i]); <span class="hljs-comment">//这里返回的是数组,直接打印即可</span>
- }
- </code></pre>
- <p>改1 中,我们让匿名函数进行自我执行,导致最终返回给a[i]的是数组而不是函数了。
- 最终导致b[0]-b[4]中保留了0,1,2,3,4 的值。</p>
- <h3 id="循环里包含匿名函数-改2,匿名函数下再做个匿名函">循环里包含匿名函数-改2,匿名函数下再做个匿名函</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> arr = [];
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++) {
- arr[i] = (<span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">num</span>) </span>{
- <span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//直接返回值,改2 变成返回函数</span>
- <span class="hljs-keyword">return</span> num; <span class="hljs-comment">//原理和改1 一样</span>
- }
- })(i);
- }
- <span class="hljs-keyword">return</span> arr;
- }
- <span class="hljs-keyword">var</span> b = box();
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i < b.length; i++) {
- alert(b[i]()); <span class="hljs-comment">//这里通过b[i]()函数调用即可</span>
- }
- </code></pre>
- <p>改1 和改2 中,我们通过匿名函数自我执行,立即把结果赋值给a[i]。每一个i,是调
- 用方通过按值传递的,所以最终返回的都是指定的递增的i。而不是box()函数里的i。
- 关于this 对象
- 在闭包中使用this 对象也可能会导致一些问题,this 对象是在运行时基于函数的执行环
- 境绑定的,如果this 在全局范围就是window,如果在对象内部就指向这个对象。而闭包却
- 在运行时指向window 的,因为闭包并不属于这个对象的属性或方法。</p>
- <pre><code class="lang-js"><span class="hljs-keyword">var</span> user = <span class="hljs-string">'The Window'</span>;
- <span class="hljs-keyword">var</span> obj = {
- user : <span class="hljs-string">'The Object'</span>,
- getUserFunction : <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//闭包不属于obj,里面的this 指向window</span>
- <span class="hljs-keyword">return</span> <span class="hljs-keyword">this</span>.user;
- };
- }
- };
- alert(obj.getUserFunction()()); <span class="hljs-comment">//The window</span>
- <span class="hljs-comment">//可以强制指向某个对象</span>
- alert(obj.getUserFunction().call(obj)); <span class="hljs-comment">//The Object</span>
- <span class="hljs-comment">//也可以从上一个作用域中得到对象</span>
- getUserFunction : <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> that = <span class="hljs-keyword">this</span>; <span class="hljs-comment">//从对象的方法里得对象</span>
- <span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> that.user;
- };
- }
- </code></pre>
- <h3 id="内存泄漏">内存泄漏</h3>
- <p>由于IE 的JScript 对象和DOM 对象使用不同的垃圾收集方式,因此闭包在IE 中会导致
- 一些问题。就是内存泄漏的问题,也就是无法销毁驻留在内存中的元素。以下代码有两个知
- 识点还没有学习到,一个是DOM,一个是事件。</p>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> oDiv = <span class="hljs-built_in">document</span>.getElementById(<span class="hljs-string">'oDiv'</span>); <span class="hljs-comment">//oDiv 用完之后一直驻留在内存</span>
- oDiv.onclick = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- alert(oDiv.innerHTML); <span class="hljs-comment">//这里用oDiv 导致内存泄漏</span>
- };
- }
- box();
- </code></pre>
- <p>那么在最后应该将oDiv 解除引用来避免内存泄漏。</p>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> oDiv = <span class="hljs-built_in">document</span>.getElementById(<span class="hljs-string">'oDiv'</span>);
- <span class="hljs-keyword">var</span> text = oDiv.innerHTML;
- oDiv.onclick = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- alert(text);
- };
- oDiv = <span class="hljs-literal">null</span>; <span class="hljs-comment">//解除引用</span>
- }
- </code></pre>
- <p>PS:如果并没有使用解除引用,那么需要等到浏览器关闭才得以释放。
- 模仿块级作用域
- JavaScript 没有块级作用域的概念。</p>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params">count</span>) </span>{
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i=<span class="hljs-number">0</span>; i<count; i++) {}
- alert(i); <span class="hljs-comment">//i 不会因为离开了for 块就失效</span>
- }
- box(<span class="hljs-number">2</span>);
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params">count</span>) </span>{
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i=<span class="hljs-number">0</span>; i<count; i++) {}
- <span class="hljs-keyword">var</span> i; <span class="hljs-comment">//就算重新声明,也不会前面的值</span>
- alert(i);
- }
- box(<span class="hljs-number">2</span>);
- </code></pre>
- <p>以上两个例子,说明JavaScript 没有块级语句的作用域,if () {} for () {}等没有作用域,
- 如果有,出了这个范围i 就应该被销毁了。就算重新声明同一个变量也不会改变它的值。
- JavaScript 不会提醒你是否多次声明了同一个变量;遇到这种情况,它只会对后续的声
- 明视而不见(如果初始化了,当然还会执行的)。使用模仿块级作用域可避免这个问题。</p>
- <h3 id="模仿块级作用域私有作用域">模仿块级作用域(私有作用域)</h3>
- <pre><code class="lang-js">(<span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-comment">//这里是块级作用域</span>
- })();
- <span class="hljs-comment">//使用块级作用域(私有作用域)改写</span>
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params">count</span>) </span>{
- (<span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> i = <span class="hljs-number">0</span>; i<count; i++) {}
- })();
- alert(i); <span class="hljs-comment">//报错,无法访问</span>
- }
- box(<span class="hljs-number">2</span>);
- </code></pre>
- <p>使用了块级作用域(私有作用域)后,匿名函数中定义的任何变量,都会在执行结束时被
- 销毁。这种技术经常在全局作用域中被用在函数外部,从而限制向全局作用域中添加过多的
- 变量和函数。一般来说,我们都应该尽可能少向全局作用域中添加变量和函数。在大型项目
- 中,多人开发的时候,过多的全局变量和函数很容易导致命名冲突,引起灾难性的后果。如
- 果采用块级作用域(私有作用域),每个开发者既可以使用自己的变量,又不必担心搞乱全局
- 作用域。</p>
- <pre><code class="lang-js">(<span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> box = [<span class="hljs-number">1</span>,<span class="hljs-number">2</span>,<span class="hljs-number">3</span>,<span class="hljs-number">4</span>];
- alert(box); <span class="hljs-comment">//box 出来就不认识了</span>
- })();
- </code></pre>
- <p>在全局作用域中使用块级作用域可以减少闭包占用的内存问题,因为没有指向匿名函数
- 的引用。只要函数执行完毕,就可以立即销毁其作用域链了。
- 私有变量
- JavaScript 没有私有属性的概念;所有的对象属性都是公有的。不过,却有一个私有变
- 量的概念。任何在函数中定义的变量,都可以认为是私有变量,因为不能在函数的外部访问
- 这些变量。</p>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>; <span class="hljs-comment">//私有变量,外部无法访问</span>
- }
- </code></pre>
- <p>而通过函数内部创建一个闭包,那么闭包通过自己的作用域链也可以访问这些变量。而
- 利用这一点,可以创建用于访问私有变量的公有方法。</p>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">Box</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>; <span class="hljs-comment">//私有变量</span>
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">run</span>(<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//私有函数</span>
- <span class="hljs-keyword">return</span> <span class="hljs-string">'运行中...'</span>;
- }
- <span class="hljs-keyword">this</span>.get = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//对外公共的特权方法</span>
- <span class="hljs-keyword">return</span> age + run();
- };
- }
- <span class="hljs-keyword">var</span> box = <span class="hljs-keyword">new</span> Box();
- alert(box.get());
- </code></pre>
- <h3 id="可以通过构造方法传参来访问私有变量">可以通过构造方法传参来访问私有变量</h3>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">Person</span>(<span class="hljs-params">value</span>) </span>{
- <span class="hljs-keyword">var</span> user = value; <span class="hljs-comment">//这句其实可以省略</span>
- <span class="hljs-keyword">this</span>.getUser = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> user;
- };
- <span class="hljs-keyword">this</span>.setUser = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">value</span>) </span>{
- user = value;
- };
- }
- </code></pre>
- <p>但是对象的方法,在多次调用的时候,会多次创建。可以使用静态私有变量来避免这个
- 问题。
- 静态私有变量
- 通过块级作用域(私有作用域)中定义私有变量或函数,同样可以创建对外公共的特权方
- 法。</p>
- <pre><code class="lang-js">(<span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>;
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">run</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> <span class="hljs-string">'运行中...'</span>;
- }
- Box = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{}; <span class="hljs-comment">//构造方法</span>
- Box.prototype.go = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//原型方法</span>
- <span class="hljs-keyword">return</span> age + run();
- };
- })();
- <span class="hljs-keyword">var</span> box = <span class="hljs-keyword">new</span> Box();
- alert(box.go());
- </code></pre>
- <p>上面的对象声明,采用的是Box = function () {} 而不是function Box() {} 因为如果用后
- 面这种,就变成私有函数了,无法在全局访问到了,所以使用了前面这种。</p>
- <pre><code class="lang-js">(<span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> user = <span class="hljs-string">''</span>;
- Person = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">value</span>) </span>{
- user = value;
- };
- Person.prototype.getUser = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> user;
- };
- Person.prototype.setUser = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">value</span>) </span>{
- user = value;
- }
- })();
- </code></pre>
- <p>使用了prototype 导致方法共享了,而user 也就变成静态属性了。(所谓静态属性,即共
- 享于不同对象中的属性)。
- 模块模式
- 之前采用的都是构造函数的方式来创建私有变量和特权方法。那么对象字面量方式就采
- 用模块模式来创建。</p>
- <pre><code class="lang-js"><span class="hljs-keyword">var</span> box = { <span class="hljs-comment">//字面量对象,也是单例对象</span>
- age : <span class="hljs-number">100</span>, <span class="hljs-comment">//这是公有属性,将要改成私有</span>
- run : <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{ <span class="hljs-comment">//这时公有函数,将要改成私有</span>
- <span class="hljs-keyword">return</span> <span class="hljs-string">'运行中...'</span>;
- };
- };
- </code></pre>
- <h3 id="私有化变量和函数">私有化变量和函数</h3>
- <pre><code class="lang-js"><span class="hljs-keyword">var</span> box = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>;
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">run</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> <span class="hljs-string">'运行中...'</span>;
- }
- <span class="hljs-keyword">return</span> { <span class="hljs-comment">//直接返回对象</span>
- go : <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> age + run();
- }
- };
- }();
- </code></pre>
- <p>上面的直接返回对象的例子,也可以这么写</p>
- <pre><code class="lang-js"><span class="hljs-keyword">var</span> box = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>;
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">run</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> <span class="hljs-string">'运行中...'</span>;
- }
- <span class="hljs-keyword">var</span> obj = { <span class="hljs-comment">//创建字面量对象</span>
- go : <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> age + run();
- }
- };
- <span class="hljs-keyword">return</span> obj; <span class="hljs-comment">//返回这个对象</span>
- }();
- </code></pre>
- <p>字面量的对象声明,其实在设计模式中可以看作是一种单例模式,所谓单例模式,就是
- 永远保持对象的一个实例。
- 增强的模块模式,这种模式适合返回自定义对象,也就是构造函数。</p>
- <pre><code class="lang-js"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">Desk</span>(<span class="hljs-params"></span>) </span>{};
- <span class="hljs-keyword">var</span> box = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">var</span> age = <span class="hljs-number">100</span>;
- <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">run</span>(<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> <span class="hljs-string">'运行中...'</span>;
- }
- <span class="hljs-keyword">var</span> desk = <span class="hljs-keyword">new</span> Desk(); <span class="hljs-comment">//可以实例化特定的对象</span>
- desk.go = <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
- <span class="hljs-keyword">return</span> age + run();
- };
- <span class="hljs-keyword">return</span> desk;
- }();
- alert(box.go());
- </code></pre>
- </blockquote>
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