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<a href="/2019/02/28/vue-slots-and-scopedslots/" class="post-title-link" itemprop="url">vm.$slots和vm.$scopedSlots 在渲染函数内的使用</a>
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<p>以下例子是在 <a href="mailto:[email protected]" target="_blank" rel="noopener">[email protected]</a> 中运行的。</p>
<p><code>vm.$slots</code> 与 <code>vm.$scopedSlots</code> 是两个与插槽相关的属性。在使用渲染函数替代 vue 的模板功能时我们可能需要用到这两个属性来实现插槽的功能。</p>
<p>下面利用一个例子来研究 <code>vm.$slots</code> <code>vm.$scopedSlots</code> 的区别。</p>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- App.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">template</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span> <span class="attr">id</span>=<span class="string">"app"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">HelloWorld</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">h1</span> <span class="attr">slot</span>=<span class="string">"head"</span> <span class="attr">slot-scope</span>=<span class="string">"{author}"</span>></span>this is head slot -- {{author}}<span class="tag"></<span class="name">h1</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span>></span>this is default slot<span class="tag"></<span class="name">div</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span> <span class="attr">slot</span>=<span class="string">"foot"</span>></span>this is foot slot<span class="tag"></<span class="name">div</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">HelloWorld</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">div</span>></span></span><br><span class="line"><span class="tag"></<span class="name">template</span>></span></span><br><span class="line"></span><br><span class="line"><span class="comment"><!-- 后面代码 略 --></span></span><br></pre></td></tr></table></figure>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- HelloWorld.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">template</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span> <span class="attr">class</span>=<span class="string">"hello"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">slot</span> <span class="attr">name</span>=<span class="string">"head"</span> <span class="attr">author</span>=<span class="string">"Allen"</span>></span><span class="tag"></<span class="name">slot</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">slot</span> <span class="attr">name</span>=<span class="string">"aside"</span>></span><span class="tag"></<span class="name">slot</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">slot</span>></span><span class="tag"></<span class="name">slot</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">slot</span> <span class="attr">name</span>=<span class="string">"foot"</span>></span><span class="tag"></<span class="name">slot</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">div</span>></span></span><br><span class="line"><span class="tag"></<span class="name">template</span>></span></span><br><span class="line"></span><br><span class="line"><span class="comment"><!-- 后面代码 略 --></span></span><br></pre></td></tr></table></figure>
<p>我们在 <code>HelloWorld.vue</code> 内定义三个具名插槽和一个默认插槽。在 <code>App.vue</code> 内实例化 HelloWorld 组件时，只使用了 <code>head</code> <code>default</code> <code>foot</code> 插槽，其中 <code>head</code> 插槽是一个作用域插槽。</p>
<p>然后我们将 <code>vm.$slots</code> <code>vm.$scopedSlots</code>打印的到控制台上，chrome 浏览器上打印的结果如下：</p>
<h4 id="vm-slots"><a href="#vm-slots" class="headerlink" title="vm.\$slots"></a>vm.\$slots</h4><p><img src="https://note.youdao.com/yws/res/4098/EB147A0005BE49C4BE7E572B7767079F" alt="vm.$slots"></p>
<p>观察发现</p>
<ul>
<li>只有被使用到的插槽才会出现在 <code>vm.$slots</code> 内。</li>
<li>默认插槽和具名插槽的值是虚拟 dom 数组（<code>VNode[]</code>）,作用域插槽对应的值是一个 <code>get</code> 方法且属性修饰为不可枚举。</li>
</ul>
<h4 id="vm-scopedSlots"><a href="#vm-scopedSlots" class="headerlink" title="vm.\$scopedSlots"></a>vm.\$scopedSlots</h4><p><img src="https://note.youdao.com/yws/res/4100/F15683549E22485EBEED1246DCB44F0E" alt="vm.$scopedSlots"></p>
<p>观察发现</p>
<ul>
<li>只有被使用到的插槽才会出现在 <code>vm.$scopedSlots</code> 内。</li>
<li>这里面多了 <code>$stable</code> <code>_normalized</code> 属性。具体什么作用，未知。</li>
<li>无论是具名插槽、默认插槽、作用域插槽都在，而且值是一个工厂函数，调用后会返回虚拟 dom 数组（<code>VNode[]</code>）。</li>
<li>作用域插槽对应的函数内多个参数 <code>scope</code>，可以通过它将参数传给插槽。</li>
<li>所有值都是可枚举的。</li>
</ul>
<h2 id="vm-slots-在开发中的使用"><a href="#vm-slots-在开发中的使用" class="headerlink" title="vm.\$slots 在开发中的使用"></a>vm.\$slots 在开发中的使用</h2><p>以下例子来自 Vue 官方文档，仅做了些许的改动。</p>
<h3 id="简单的例子"><a href="#简单的例子" class="headerlink" title="简单的例子"></a>简单的例子</h3><figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- MyHeadline.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">script</span>></span><span class="undefined"></span></span><br><span class="line"><span class="javascript"> <span class="keyword">export</span> <span class="keyword">default</span> {</span></span><br><span class="line"><span class="javascript"> name: <span class="string">"MyHeadline"</span>,</span></span><br><span class="line"><span class="undefined"> props: {</span></span><br><span class="line"><span class="undefined"> level: {</span></span><br><span class="line"><span class="javascript"> type: <span class="built_in">Number</span>,</span></span><br><span class="line"><span class="javascript"> required: <span class="literal">true</span></span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> },</span></span><br><span class="line"><span class="undefined"> render(createElement) {</span></span><br><span class="line"><span class="javascript"> <span class="keyword">return</span> createElement(<span class="string">"h"</span> + <span class="keyword">this</span>.level, <span class="keyword">this</span>.$slots.default);</span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> };</span></span><br><span class="line"><span class="undefined"></span><span class="tag"></<span class="name">script</span>></span></span><br></pre></td></tr></table></figure>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- App.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">template</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span> <span class="attr">id</span>=<span class="string">"app"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">MyHeadline</span> <span class="attr">:level</span>=<span class="string">"1"</span>></span>这是level 1<span class="tag"></<span class="name">MyHeadline</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">MyHeadline</span> <span class="attr">:level</span>=<span class="string">"2"</span>></span>这是level 2<span class="tag"></<span class="name">MyHeadline</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">MyHeadline</span> <span class="attr">:level</span>=<span class="string">"3"</span>></span>这是level 3<span class="tag"></<span class="name">MyHeadline</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">MyHeadline</span> <span class="attr">:level</span>=<span class="string">"4"</span>></span>这是level 4<span class="tag"></<span class="name">MyHeadline</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">MyHeadline</span> <span class="attr">:level</span>=<span class="string">"5"</span>></span>这是level 5<span class="tag"></<span class="name">MyHeadline</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">MyHeadline</span> <span class="attr">:level</span>=<span class="string">"6"</span>></span>这是level 6<span class="tag"></<span class="name">MyHeadline</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">div</span>></span></span><br><span class="line"><span class="tag"></<span class="name">template</span>></span></span><br><span class="line"></span><br><span class="line"><span class="comment"><!-- 后面代码 略 --></span></span><br></pre></td></tr></table></figure>
<p>页面渲染的结果：</p>
<p><img src="https://note.youdao.com/yws/res/4101/0E93C9D17EF543CAAD51705E67B781ED" alt="渲染结果"></p>
<p>页面的 html 结构：</p>
<p><img src="https://note.youdao.com/yws/res/4099/CCAF184EDE8348D7A9047FED4DE328E1" alt="html结构"></p>
<p><code>MyHeadline</code> 组件的目的很明显，就是根据传入的 <code>level</code> 属性生成对应级别的 h 标签。使用 vue 的模板是很难实现这样的功能的，所以这里用到了 vue 的渲染函数（其实 vue 模板最终也是编译成渲染函数）。</p>
<h3 id="进阶例子"><a href="#进阶例子" class="headerlink" title="进阶例子"></a>进阶例子</h3><figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- AnchoredHeading.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">script</span>></span><span class="undefined"></span></span><br><span class="line"><span class="javascript"> <span class="keyword">var</span> getChildrenTextContent = <span class="function"><span class="keyword">function</span>(<span class="params">children</span>) </span>{</span></span><br><span class="line"><span class="javascript"> <span class="keyword">return</span> children</span></span><br><span class="line"><span class="javascript"> .map(<span class="function"><span class="keyword">function</span>(<span class="params">node</span>) </span>{</span></span><br><span class="line"><span class="javascript"> <span class="keyword">return</span> node.children</span></span><br><span class="line"><span class="undefined"> ? getChildrenTextContent(node.children)</span></span><br><span class="line"><span class="undefined"> : node.text;</span></span><br><span class="line"><span class="undefined"> })</span></span><br><span class="line"><span class="javascript"> .join(<span class="string">""</span>);</span></span><br><span class="line"><span class="undefined"> };</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript"> <span class="keyword">export</span> <span class="keyword">default</span> {</span></span><br><span class="line"><span class="javascript"> name: <span class="string">"AnchoredHeading"</span>,</span></span><br><span class="line"><span class="undefined"> props: {</span></span><br><span class="line"><span class="undefined"> level: {</span></span><br><span class="line"><span class="javascript"> type: <span class="built_in">Number</span>,</span></span><br><span class="line"><span class="javascript"> required: <span class="literal">true</span></span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> },</span></span><br><span class="line"><span class="undefined"> render(createElement) {</span></span><br><span class="line"><span class="javascript"> <span class="comment">// 创建 kebab-case 风格的ID</span></span></span><br><span class="line"><span class="javascript"> <span class="keyword">var</span> headingId = getChildrenTextContent(<span class="keyword">this</span>.$slots.default)</span></span><br><span class="line"><span class="undefined"> .toLowerCase()</span></span><br><span class="line"><span class="javascript"> .replace(<span class="regexp">/\W+/g</span>, <span class="string">"-"</span>)</span></span><br><span class="line"><span class="javascript"> .replace(<span class="regexp">/(^\-|\-$)/g</span>, <span class="string">""</span>);</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript"> <span class="keyword">return</span> createElement(<span class="string">"h"</span> + <span class="keyword">this</span>.level, [</span></span><br><span class="line"><span class="undefined"> createElement(</span></span><br><span class="line"><span class="javascript"> <span class="string">"a"</span>,</span></span><br><span class="line"><span class="undefined"> {</span></span><br><span class="line"><span class="undefined"> attrs: {</span></span><br><span class="line"><span class="undefined"> name: headingId,</span></span><br><span class="line"><span class="javascript"> href: <span class="string">"#"</span> + headingId</span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> },</span></span><br><span class="line"><span class="javascript"> <span class="keyword">this</span>.$slots.default</span></span><br><span class="line"><span class="undefined"> )</span></span><br><span class="line"><span class="undefined"> ]);</span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> };</span></span><br><span class="line"><span class="undefined"></span><span class="tag"></<span class="name">script</span>></span></span><br></pre></td></tr></table></figure>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- App.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">template</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span> <span class="attr">id</span>=<span class="string">"app"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">AnchoredHeading</span> <span class="attr">:level</span>=<span class="string">"1"</span>></span>chapter 1 love<span class="tag"></<span class="name">AnchoredHeading</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">AnchoredHeading</span> <span class="attr">:level</span>=<span class="string">"2"</span>></span>chapter 2 marry<span class="tag"></<span class="name">AnchoredHeading</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">AnchoredHeading</span> <span class="attr">:level</span>=<span class="string">"3"</span>></span>chapter 3 rival<span class="tag"></<span class="name">AnchoredHeading</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">AnchoredHeading</span> <span class="attr">:level</span>=<span class="string">"4"</span>></span>chapter 4 hate<span class="tag"></<span class="name">AnchoredHeading</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">AnchoredHeading</span> <span class="attr">:level</span>=<span class="string">"5"</span>></span>chapter 5 divorce<span class="tag"></<span class="name">AnchoredHeading</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">AnchoredHeading</span> <span class="attr">:level</span>=<span class="string">"6"</span>></span>chapter 6 真香<span class="tag"></<span class="name">AnchoredHeading</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">div</span>></span></span><br><span class="line"><span class="tag"></<span class="name">template</span>></span></span><br><span class="line"></span><br><span class="line"><span class="comment"><!-- 后面代码 略 --></span></span><br></pre></td></tr></table></figure>
<p>页面渲染结果：</p>
<p><img src="https://note.youdao.com/yws/res/4137/D580782D95F743839C502CDDFFC17897" alt="渲染结果2"></p>
<p>页面 html 结构：</p>
<p><img src="https://note.youdao.com/yws/res/4136/19E72031A54E4B6DAD7A7B8B21D9C002" alt="html结构2"></p>
<h2 id="vm-scopedSlots-在开发中的使用"><a href="#vm-scopedSlots-在开发中的使用" class="headerlink" title="vm.\$scopedSlots 在开发中的使用"></a>vm.\$scopedSlots 在开发中的使用</h2><h3 id="简单例子"><a href="#简单例子" class="headerlink" title="简单例子"></a>简单例子</h3><figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- Menu.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">script</span>></span><span class="undefined"></span></span><br><span class="line"><span class="javascript"> <span class="keyword">export</span> <span class="keyword">default</span> {</span></span><br><span class="line"><span class="javascript"> name: <span class="string">"Menu"</span>,</span></span><br><span class="line"><span class="undefined"> render(createElement) {</span></span><br><span class="line"><span class="javascript"> <span class="keyword">return</span> createElement(</span></span><br><span class="line"><span class="javascript"> <span class="string">"div"</span>,</span></span><br><span class="line"><span class="javascript"> { <span class="attr">class</span>: <span class="string">"menuBox"</span> },</span></span><br><span class="line"><span class="javascript"> <span class="keyword">this</span>.$scopedSlots.default({ <span class="attr">title</span>: <span class="string">"🌎 菜单栏目 🌎"</span> })</span></span><br><span class="line"><span class="undefined"> );</span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> };</span></span><br><span class="line"><span class="undefined"></span><span class="tag"></<span class="name">script</span>></span></span><br></pre></td></tr></table></figure>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- MenuItem.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">script</span>></span><span class="undefined"></span></span><br><span class="line"><span class="javascript"> <span class="keyword">export</span> <span class="keyword">default</span> {</span></span><br><span class="line"><span class="javascript"> name: <span class="string">"MenuItem"</span>,</span></span><br><span class="line"><span class="undefined"> render(createElement) {</span></span><br><span class="line"><span class="javascript"> <span class="keyword">return</span> createElement(<span class="string">"div"</span>, { <span class="attr">class</span>: <span class="string">"MenuItem"</span> }, <span class="keyword">this</span>.$slots.default);</span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> };</span></span><br><span class="line"><span class="undefined"></span><span class="tag"></<span class="name">script</span>></span></span><br></pre></td></tr></table></figure>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- App.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">template</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span> <span class="attr">id</span>=<span class="string">"app"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">menu</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">template</span> <span class="attr">slot-scope</span>=<span class="string">"{title}"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">h4</span>></span>{{title}}<span class="tag"></<span class="name">h4</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">menuitem</span>></span>首页<span class="tag"></<span class="name">menuitem</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">menuitem</span>></span>产品<span class="tag"></<span class="name">menuitem</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">menuitem</span>></span>公司简介<span class="tag"></<span class="name">menuitem</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">menuitem</span>></span>联系我们<span class="tag"></<span class="name">menuitem</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">template</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">menu</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">div</span>></span></span><br><span class="line"><span class="tag"></<span class="name">template</span>></span></span><br><span class="line"></span><br><span class="line"><span class="comment"><!-- 后面代码 略 --></span></span><br></pre></td></tr></table></figure>
<p>在<code>Menu.vue</code>内我们通过<code>this.$scopedSlots.default({ title: "🌎 菜单栏目 🌎" })</code>向作用域插槽传了参数（<code>{ title: "🌎 菜单栏目 🌎" }</code>）。然后我们在 <code>App.vue</code> 内使用 <code><template slot-scope="{title}"></code> 获得传过来的参数（这里用了解构赋值）。</p>
<p>上面只是为了展示<code>vm.$scopedSlots</code>在渲染函数内的使用，这个例子内的行为有点多此一举。</p>
<p>页面渲染结果：</p>
<p><img src="https://note.youdao.com/yws/res/4468/WEBRESOURCE882982210635beeed57bdfff7154dfb8" alt="scopedslots渲染结果.png"></p>
<p>页面 html 结构：</p>
<p><img src="https://note.youdao.com/yws/res/4470/WEBRESOURCE178ed95b3ed30d5d2c691c508c683530" alt="scopedslots_html结构.png"></p>
<h3 id="在渲染函数内插入作用域插槽"><a href="#在渲染函数内插入作用域插槽" class="headerlink" title="在渲染函数内插入作用域插槽"></a>在渲染函数内插入作用域插槽</h3><p>如果我们把上面那个例子里<code>App.vue</code>的模板写法改成渲染函数的话，我们该如何插入作用域插槽呢？</p>
<p>在模板写法内插入插槽很简单，只要在组件标签内插入即可。在渲染函数内需要用到<code>createElement</code>方法内的<code>scopedSlots</code>选项。</p>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"><!-- App.vue --></span></span><br><span class="line"></span><br><span class="line"><span class="tag"><<span class="name">script</span>></span><span class="undefined"></span></span><br><span class="line"><span class="javascript"> <span class="keyword">import</span> Menu <span class="keyword">from</span> <span class="string">"./components/Menu.vue"</span>;</span></span><br><span class="line"><span class="javascript"> <span class="keyword">import</span> MenuItem <span class="keyword">from</span> <span class="string">"./components/MenuItem.vue"</span>;</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="javascript"> <span class="keyword">export</span> <span class="keyword">default</span> {</span></span><br><span class="line"><span class="javascript"> name: <span class="string">"app"</span>,</span></span><br><span class="line"><span class="undefined"> components: {</span></span><br><span class="line"><span class="undefined"> Menu,</span></span><br><span class="line"><span class="undefined"> MenuItem</span></span><br><span class="line"><span class="undefined"> },</span></span><br><span class="line"><span class="undefined"> render(createElement) {</span></span><br><span class="line"><span class="javascript"> <span class="keyword">return</span> createElement(<span class="string">"div"</span>, { <span class="attr">attrs</span>: { <span class="attr">id</span>: <span class="string">"app"</span> } }, [</span></span><br><span class="line"><span class="javascript"> createElement(<span class="string">"Menu"</span>, {</span></span><br><span class="line"><span class="undefined"> scopedSlots: {</span></span><br><span class="line"><span class="javascript"> <span class="keyword">default</span>: <span class="function">(<span class="params">{ title }</span>) =></span> {</span></span><br><span class="line"><span class="javascript"> <span class="keyword">return</span> [</span></span><br><span class="line"><span class="javascript"> createElement(<span class="string">"h4"</span>, title),</span></span><br><span class="line"><span class="javascript"> createElement(<span class="string">"MenuItem"</span>, <span class="string">"首页"</span>),</span></span><br><span class="line"><span class="javascript"> createElement(<span class="string">"MenuItem"</span>, <span class="string">"产品"</span>),</span></span><br><span class="line"><span class="javascript"> createElement(<span class="string">"MenuItem"</span>, <span class="string">"公司简介"</span>),</span></span><br><span class="line"><span class="javascript"> createElement(<span class="string">"MenuItem"</span>, <span class="string">"联系我们"</span>)</span></span><br><span class="line"><span class="undefined"> ];</span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> })</span></span><br><span class="line"><span class="undefined"> ]);</span></span><br><span class="line"><span class="undefined"> }</span></span><br><span class="line"><span class="undefined"> };</span></span><br><span class="line"><span class="undefined"></span><span class="tag"></<span class="name">script</span>></span></span><br></pre></td></tr></table></figure>
<p>这个写法和上面的模板写法的效果是等同的。</p>
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<p><code>Object.defineProperty</code> 可以给对象定义属性,以及属性的描述。</p>
<h2 id="基本使用方法"><a href="#基本使用方法" class="headerlink" title="基本使用方法"></a>基本使用方法</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> person = { <span class="attr">name</span>: <span class="string">"Allen"</span> };</span><br><span class="line"></span><br><span class="line"><span class="comment">// 定义属性 'gender'</span></span><br><span class="line"><span class="comment">// 可配置(configurable)</span></span><br><span class="line"><span class="comment">// 可枚举(enumerable)</span></span><br><span class="line"><span class="comment">// 可写(writable)</span></span><br><span class="line"><span class="built_in">Object</span>.defineProperty(person, <span class="string">"gender"</span>, {</span><br><span class="line"> configurable: <span class="literal">true</span>,</span><br><span class="line"> enumerable: <span class="literal">true</span>,</span><br><span class="line"> writable: <span class="literal">true</span>,</span><br><span class="line"> value: <span class="string">"man"</span></span><br><span class="line">});</span><br><span class="line"></span><br><span class="line"><span class="comment">// 定义'_birthday'</span></span><br><span class="line"><span class="comment">// 我们希望生日是不可改写的，</span></span><br><span class="line"><span class="comment">// 也不希望枚举对象的时候出现它</span></span><br><span class="line"><span class="built_in">Object</span>.defineProperty(person, <span class="string">"_birthday"</span>, {</span><br><span class="line"> configurable: <span class="literal">false</span>,</span><br><span class="line"> enumerable: <span class="literal">false</span>,</span><br><span class="line"> writable: <span class="literal">false</span>,</span><br><span class="line"> value: <span class="keyword">new</span> <span class="built_in">Date</span>(<span class="string">"2000-03-03"</span>)</span><br><span class="line">});</span><br><span class="line"></span><br><span class="line"><span class="comment">// 定义'age'</span></span><br><span class="line"><span class="comment">// 年龄是通过生日获得的，并且不可改，</span></span><br><span class="line"><span class="comment">// 所以只需要设置get方法</span></span><br><span class="line"><span class="built_in">Object</span>.defineProperty(person, <span class="string">"age"</span>, {</span><br><span class="line"> configurable: <span class="literal">false</span>,</span><br><span class="line"> enumerable: <span class="literal">true</span>,</span><br><span class="line"> <span class="keyword">get</span>() {</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">new</span> <span class="built_in">Date</span>().getFullYear() - <span class="keyword">this</span>._birthday.getFullYear();</span><br><span class="line"> }</span><br><span class="line">});</span><br></pre></td></tr></table></figure>
<ul>
<li><code>configurable</code> 设置属性描述是否可修改。如果为 false,将无法对 <code>configurable</code> <code>enumerable</code> <code>writable</code> 的值进行修改。有一点例外： 当 <code>writable</code> 为 true 时，可以将其改为 false。</li>
<li><code>enumerable</code> 设置属性是否会在枚举的过程中出现。<code>for..in</code> <code>Object.keys</code> <code>Object.values</code> <code>Object.entries</code> 只会枚举属性描述 <code>enumerable</code> 为 true 的属性。其中 <code>for..in</code> 会将原型链上所有可枚举属性都遍历一遍。</li>
<li><code>writable</code> 设置属性是否可写。以上面的 <code>person</code> 对象为例，其中的 <code>_birthday</code> 属性是不可写的，假如你对它赋值（<code>person._birthday = new Date('2019-03-03')</code>）会没有效果，如果在严格模式下还会抛出异常。</li>
<li><code>value</code> 设置属性的值。</li>
<li><code>get</code> 读取属性的值。以上面 <code>person</code> 对象为例，当使用者要获取 <code>age</code> 的值时（<code>person.age</code>），获取的值就是 <code>get</code> 方法返回的值。</li>
<li><code>set</code> 写入属性的值。如果只有 <code>get</code> 没有 <code>set</code> 那么这个属性是不可写的。</li>
</ul>
<p>注意 <code>writable</code> <code>value</code>是一对，<code>get</code>方法 <code>set</code>方法是一对。有 <code>value</code> 就没有 <code>get</code> <code>set</code>。</p>
<h2 id="获取一个属性的描述"><a href="#获取一个属性的描述" class="headerlink" title="获取一个属性的描述"></a>获取一个属性的描述</h2><p>如果我们想知道一个属性描述可以使用 <code>Object.getOwnPropertyDescriptor</code>。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Object</span>.getOwnPropertyDescriptor(person, <span class="string">"age"</span>);</span><br></pre></td></tr></table></figure>
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<p>在 generator 函数内部，通过<code>yield*</code>语句，可以将<code>yield</code>委托给其他任何实现<code>iterable</code>的对象。</p>
<h3 id="委托给-generator-函数生成的iterable对象"><a href="#委托给-generator-函数生成的iterable对象" class="headerlink" title="委托给 generator 函数生成的iterable对象"></a>委托给 generator 函数生成的<code>iterable</code>对象</h3><p>调用 generator 函数会返回一个实现<code>iterable</code>的对象(该对象同时也是一个<code>iterator</code>)。</p>
<p>通过<code>yield* otherGenerator()</code>可以将 generator 内的<code>yield</code>委托给其他 generator 生成的<code>iterable</code>对象。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">foo</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"*foo() starting"</span>);</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"foo 1"</span>;</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"foo 2"</span>;</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"*foo() finished"</span>);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">bar</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"bar 1"</span>;</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"bar 2"</span>;</span><br><span class="line"> <span class="keyword">yield</span>* foo(); <span class="comment">// `yield`-delegation!</span></span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"bar 3"</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> it = bar();</span><br><span class="line"></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// "bar 1"</span></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// "bar 2"</span></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// *foo() starting</span></span><br><span class="line"><span class="comment">// "foo 1"</span></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// "foo 2"</span></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// *foo() finished</span></span><br><span class="line"><span class="comment">// "bar 3"</span></span><br></pre></td></tr></table></figure>
<p>可以看到上面的代码中，在调用第 3 个<code>next</code>方法时返回的是<code>foo</code>里面<code>yield</code>的<code>"foo 1"</code>；在调用第 5 个<code>next</code>时，并没有返回<code>foo</code> generator 隐式<code>return</code>的<code>undefined</code>,而是返回了<code>"bar 3"</code>。</p>
<p>如果<code>foo</code>内有显式的<code>return</code>语句，那么在进行 yield-delegation 时是否会返回<code>foo</code> <code>return</code>的值吗？</p>
<p>下面的代码在<code>foo</code>中添加了一个<code>return</code>语句。在<code>bar</code>内将<code>yield* foo()</code>表达式的值赋值给<code>tmp</code>变量并打印。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">foo</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"*foo() starting"</span>);</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"foo 1"</span>;</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"foo 2"</span>;</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"*foo() finished"</span>);</span><br><span class="line"> <span class="keyword">return</span> <span class="string">"foo 3"</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">bar</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"bar 1"</span>;</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"bar 2"</span>;</span><br><span class="line"> <span class="keyword">var</span> tmp = <span class="keyword">yield</span>* foo(); <span class="comment">// `yield`-delegation!</span></span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"在bar内打印"</span>, tmp);</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"bar 3"</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> it = bar();</span><br><span class="line"></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// "bar 1"</span></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// "bar 2"</span></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// *foo() starting</span></span><br><span class="line"><span class="comment">// "foo 1"</span></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// "foo 2"</span></span><br><span class="line">it.next().value;</span><br><span class="line"><span class="comment">// *foo() finished</span></span><br><span class="line"><span class="comment">// 在bar内打印 foo 3</span></span><br><span class="line"><span class="comment">// "bar 3"</span></span><br></pre></td></tr></table></figure>
<p>在第 5 次调用<code>next</code>方法时，可以发现<code>foo</code> <code>return</code>的<code>"foo 3"</code>变成了<code>yield* foo()</code>表达式的值，并被打印为<code>"在bar内打印 foo 3"</code>;<code>"bar 3"</code>成为<code>next</code>方法的返回值。</p>
<h3 id="委托给其他任何实现iterable的对象"><a href="#委托给其他任何实现iterable的对象" class="headerlink" title="委托给其他任何实现iterable的对象"></a>委托给其他任何实现<code>iterable</code>的对象</h3><p>generator 内部的<code>yield*</code>语句也能将<code>yield</code>委托给其他非 generator 生成的<code>iterable</code>对象。例如 数组就是一个实现了<code>iterable</code>的对象。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">bar</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"inside `*bar()`:"</span>, <span class="keyword">yield</span> <span class="string">"A"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// `yield`-delegation to a non-generator!</span></span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"inside `*bar()`:"</span>, <span class="keyword">yield</span>* [<span class="string">"B"</span>, <span class="string">"C"</span>, <span class="string">"D"</span>]);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"inside `*bar()`:"</span>, <span class="keyword">yield</span> <span class="string">"E"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> <span class="string">"F"</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> it = bar();</span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next().value);</span><br><span class="line"><span class="comment">// outside: A</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">1</span>).value);</span><br><span class="line"><span class="comment">// inside `*bar()`: 1</span></span><br><span class="line"><span class="comment">// outside: B</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">2</span>).value);</span><br><span class="line"><span class="comment">// outside: C</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">3</span>).value);</span><br><span class="line"><span class="comment">// outside: D</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">4</span>).value);</span><br><span class="line"><span class="comment">// inside `*bar()`: undefined</span></span><br><span class="line"><span class="comment">// outside: E</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">5</span>).value);</span><br><span class="line"><span class="comment">// inside `*bar()`: 5</span></span><br><span class="line"><span class="comment">// outside: F</span></span><br></pre></td></tr></table></figure>
<p>也可以委托给自己手写的<code>iterable</code>对象。由于 javascript 不是强类型语言，如果对象上含有<code>Symbol.iterator</code>方法，那么就可以将该对象当做一个<code>iterable</code>对象；如果对象上含有<code>next</code>方法，那就可以将该对象当做一个<code>iterator</code>对象。下面的<code>myIterable</code>对象即实现了<code>Symbol.iterator</code>方法也实现了<code>next</code>方法，所以它即是一个<code>iterable</code>又是一个<code>iterator</code>。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> myIterable = {</span><br><span class="line"> [<span class="built_in">Symbol</span>.iterator]: <span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">this</span>;</span><br><span class="line"> },</span><br><span class="line"> num: <span class="number">98</span>,</span><br><span class="line"> next: <span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">var</span> self = <span class="keyword">this</span>;</span><br><span class="line"> <span class="keyword">if</span> (self.num < <span class="number">101</span>) {</span><br><span class="line"> <span class="keyword">return</span> { <span class="attr">value</span>: <span class="built_in">String</span>.fromCharCode(self.num++), <span class="attr">done</span>: <span class="literal">false</span> };</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">return</span> { <span class="attr">value</span>: <span class="built_in">String</span>.fromCharCode(<span class="number">101</span>), <span class="attr">done</span>: <span class="literal">true</span> };</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">bar</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"inside `*bar()`:"</span>, <span class="keyword">yield</span> <span class="string">"A"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// `yield`-delegation to a non-generator!</span></span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"inside `*bar()`:"</span>, <span class="keyword">yield</span>* myIterable);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"inside `*bar()`:"</span>, <span class="keyword">yield</span> <span class="string">"E"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> <span class="string">"F"</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> it = bar();</span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next().value);</span><br><span class="line"><span class="comment">// outside: A</span></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">1</span>).value);</span><br><span class="line"><span class="comment">// inside `*bar()`: 1</span></span><br><span class="line"><span class="comment">// outside: b</span></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">2</span>).value);</span><br><span class="line"><span class="comment">// outside: c</span></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">3</span>).value);</span><br><span class="line"><span class="comment">// outside: d</span></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">4</span>).value);</span><br><span class="line"><span class="comment">// inside `*bar()`: e</span></span><br><span class="line"><span class="comment">// outside: E</span></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">5</span>).value);</span><br><span class="line"><span class="comment">// inside `*bar()`: 5</span></span><br><span class="line"><span class="comment">// outside: F</span></span><br></pre></td></tr></table></figure>
<h3 id="异常委托"><a href="#异常委托" class="headerlink" title="异常委托"></a>异常委托</h3><p>被委托的<code>iterator</code>内部执行过程发生异常，如果异常被捕获，那么捕获处理完异常后还按原来的逻辑运行；如果异常未被捕获，那么异常会被抛出，异常会被抛到<code>yield*</code>语句那。下面是《YOU DON’T KNOW JS》内的例子。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">foo</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"B"</span>;</span><br><span class="line"> } <span class="keyword">catch</span> (err) {</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"error caught inside `*foo()`:"</span>, err);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"C"</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">throw</span> <span class="string">"D"</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">bar</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"A"</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> <span class="keyword">yield</span>* foo();</span><br><span class="line"> } <span class="keyword">catch</span> (err) {</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"error caught inside `*bar()`:"</span>, err);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"E"</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">yield</span>* baz();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// note: can't get here!</span></span><br><span class="line"> <span class="keyword">yield</span> <span class="string">"G"</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">baz</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">throw</span> <span class="string">"F"</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> it = bar();</span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next().value);</span><br><span class="line"><span class="comment">// outside: A</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">1</span>).value);</span><br><span class="line"><span class="comment">// outside: B</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.throw(<span class="number">2</span>).value);</span><br><span class="line"><span class="comment">// error caught inside `*foo()`: 2</span></span><br><span class="line"><span class="comment">// outside: C</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">3</span>).value);</span><br><span class="line"><span class="comment">// error caught inside `*bar()`: D</span></span><br><span class="line"><span class="comment">// outside: E</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">try</span> {</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"outside:"</span>, it.next(<span class="number">4</span>).value);</span><br><span class="line">} <span class="keyword">catch</span> (err) {</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"error caught outside:"</span>, err);</span><br><span class="line">}</span><br><span class="line"><span class="comment">// error caught outside: F</span></span><br></pre></td></tr></table></figure>
<h3 id="递归委托"><a href="#递归委托" class="headerlink" title="递归委托"></a>递归委托</h3><p>下面是《YOU DON’T KNOW JS》里的例子。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">foo</span>(<span class="params">val</span>) </span>{</span><br><span class="line"> <span class="keyword">if</span> (val > <span class="number">1</span>) {</span><br><span class="line"> <span class="comment">// generator recursion</span></span><br><span class="line"> val = <span class="keyword">yield</span>* foo(val - <span class="number">1</span>);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">yield</span> request(<span class="string">"http://some.url/?v="</span> + val);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">bar</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">var</span> r1 = <span class="keyword">yield</span>* foo(<span class="number">3</span>);</span><br><span class="line"> <span class="built_in">console</span>.log(r1);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">run(bar);</span><br></pre></td></tr></table></figure>
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<p>async 函数能将 promise 链式调用的写法改成同步的写法。让代码变得更简洁易懂。es6 中的 async 是语法糖，我们自己可以实现类似 async 函数的功能。</p>
<p>下面是<code>myAsync</code>的代码：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * @param {Function} gen 一个generator函数</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">myAsync</span>(<span class="params">gen</span>) </span>{</span><br><span class="line"> <span class="keyword">var</span> args = [].slice.call(<span class="built_in">arguments</span>, <span class="number">1</span>),</span><br><span class="line"> it;</span><br><span class="line"> it = gen.apply(<span class="keyword">this</span>, args);</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params">nextVal</span>) </span>{</span><br><span class="line"> <span class="keyword">if</span> (!nextVal.done) {</span><br><span class="line"> <span class="keyword">return</span> <span class="built_in">Promise</span>.resolve(nextVal.value).then(</span><br><span class="line"> <span class="function"><span class="keyword">function</span>(<span class="params">v</span>) </span>{</span><br><span class="line"> <span class="keyword">return</span> fn(it.next(v));</span><br><span class="line"> },</span><br><span class="line"> <span class="function"><span class="keyword">function</span>(<span class="params">err</span>) </span>{</span><br><span class="line"> <span class="keyword">return</span> fn(it.throw(err));</span><br><span class="line"> }</span><br><span class="line"> );</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">return</span> <span class="built_in">Promise</span>.resolve(nextVal.value);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> fn(it.next());</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>下面是测试用例：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * 下面这个函数模拟异步请求返回一个promise</span></span><br><span class="line"><span class="comment"> * @param {String} resource 资源的路径地址</span></span><br><span class="line"><span class="comment"> * @param {Boolean} success true表示能请求成功,false表示请求失败</span></span><br><span class="line"><span class="comment"> * @returns {Promise}</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">request</span>(<span class="params">resource, success</span>) </span>{</span><br><span class="line"> <span class="keyword">var</span> randomTime = <span class="built_in">Math</span>.ceil(<span class="built_in">Math</span>.random() * <span class="number">10</span>) * <span class="number">100</span>;</span><br><span class="line"> <span class="built_in">console</span>.log(resource + <span class="string">" spend:"</span>, randomTime);</span><br><span class="line"> <span class="keyword">return</span> <span class="keyword">new</span> <span class="built_in">Promise</span>(<span class="function"><span class="keyword">function</span>(<span class="params">resolve, reject</span>) </span>{</span><br><span class="line"> setTimeout(<span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">if</span> (success) {</span><br><span class="line"> resolve(resource);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> reject(resource);</span><br><span class="line"> }</span><br><span class="line"> }, randomTime);</span><br><span class="line"> });</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * 下面的generator函数写平常的业务逻辑。</span></span><br><span class="line"><span class="comment"> * 如果下面的console.time得出来的时间与三条请求的时间之和</span></span><br><span class="line"><span class="comment"> * 大约相等，说明main函数内的代码以类似同步的方式执行。</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">main</span>(<span class="params">returnValue</span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.time(<span class="string">"count"</span>);</span><br><span class="line"> <span class="keyword">var</span> rq1 = <span class="keyword">yield</span> request(<span class="string">"/request1"</span>, <span class="literal">true</span>);</span><br><span class="line"> <span class="keyword">var</span> rq2 = <span class="keyword">yield</span> request(<span class="string">"/request2"</span>, <span class="literal">true</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> <span class="keyword">var</span> rq3 = <span class="keyword">yield</span> request(<span class="string">"/request3"</span>, <span class="literal">false</span>);</span><br><span class="line"> } <span class="keyword">catch</span> (e) {</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"this is an error"</span>, e);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">var</span> rq4 = <span class="keyword">yield</span> request(<span class="string">"/request4"</span>, <span class="literal">true</span>);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">console</span>.timeEnd(<span class="string">"count"</span>);</span><br><span class="line"> <span class="built_in">console</span>.log(returnValue);</span><br><span class="line"> <span class="keyword">return</span> returnValue;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">myAsync(main, <span class="string">"hello my async"</span>);</span><br></pre></td></tr></table></figure>
<p>可以看出<code>main</code>函数内部写法和 es6 的 async 函数很相似，相当于将<code>await</code>替换成<code>yield</code>。</p>
<p>下面是 generator 中出现<code>yield</code>-delegation 中的测试。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//这里依赖上面的 myAsync 和 request 方法</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">subTask</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">var</span> rq2 = <span class="keyword">yield</span> request(<span class="string">"/request2"</span>, <span class="literal">true</span>);</span><br><span class="line"> <span class="keyword">var</span> rq3 = <span class="keyword">yield</span> request(<span class="string">"/request3"</span>, <span class="literal">true</span>);</span><br><span class="line"> <span class="keyword">var</span> rq4 = <span class="keyword">yield</span> request(<span class="string">"/request4"</span>, <span class="literal">false</span>); <span class="comment">// promise rejected</span></span><br><span class="line"> <span class="keyword">var</span> rq5 = <span class="keyword">yield</span> request(<span class="string">"/request5"</span>, <span class="literal">true</span>);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">main</span>(<span class="params">returnValue</span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.time(<span class="string">"count"</span>);</span><br><span class="line"> <span class="keyword">var</span> rq1 = <span class="keyword">yield</span> request(<span class="string">"/request1"</span>, <span class="literal">true</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">try</span> {</span><br><span class="line"> <span class="keyword">yield</span>* subTask();</span><br><span class="line"> } <span class="keyword">catch</span> (err) {</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="string">"catch error from subTask."</span>, err);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">var</span> rq5 = <span class="keyword">yield</span> request(<span class="string">"/request6"</span>, <span class="literal">true</span>);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">console</span>.timeEnd(<span class="string">"count"</span>);</span><br><span class="line"> <span class="keyword">return</span> returnValue;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">myAsync(main, <span class="string">"hello my async"</span>);</span><br></pre></td></tr></table></figure>
<p>上面的 main 方法内<code>yield*</code>语句将<code>yield</code>委托给了 subTask 方法，并且<code>subTask</code>内 req4 的 promise 被 rejected。此时的 myAsync 还能正常运行。</p>
<p>下面是 generator 中出现递归委托的测试。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//这里依赖上面的 myAsync 和 request 方法</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">subTask</span>(<span class="params">num</span>) </span>{</span><br><span class="line"> <span class="keyword">if</span> (num < <span class="number">3</span>) {</span><br><span class="line"> <span class="keyword">yield</span>* subTask(num + <span class="number">1</span>);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">yield</span> request(<span class="string">"/request"</span> + num, <span class="literal">true</span>);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span>* <span class="title">main</span>(<span class="params">returnValue</span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.time(<span class="string">"count"</span>);</span><br><span class="line"> <span class="keyword">var</span> rq1 = <span class="keyword">yield</span> request(<span class="string">"/request1"</span>, <span class="literal">true</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">yield</span>* subTask(<span class="number">2</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">var</span> rq4 = <span class="keyword">yield</span> request(<span class="string">"/request4"</span>, <span class="literal">true</span>);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">console</span>.timeEnd(<span class="string">"count"</span>);</span><br><span class="line"> <span class="keyword">return</span> returnValue;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">myAsync(main, <span class="string">"hello my async"</span>);</span><br></pre></td></tr></table></figure>
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