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打造你的前端信息流
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2016-07-10
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<li><p><a href="https://github.com/trending?l=javascript" target="_blank" rel="external">github每日star数量排行榜</a></p>
<p>可以看到现在最火的前端开源项目。</p>
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<li><p><a href="https://www.reddit.com/r/javascript" target="_blank" rel="external">reddit社区的javascript频道</a></p>
<p>每天的javascript资讯。都是最新最火的。</p>
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<p>资讯订阅。很多大牛在上面哦！每天看看，就知道外国前端在思考那些问题。</p>
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<li><p><a href="https://medium.com/" target="_blank" rel="external">https://medium.com</a></p>
<p>资讯订阅。vue redux等多个开源项目的作者都会在这里发表文章。</p>
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<li><p><a href="http://gold.xitu.io/" target="_blank" rel="external">掘金</a></p>
<p>资讯订阅。国内比较好的技术社区。</p>
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<li><p><a href="http://www.zcfy.cc/" target="_blank" rel="external">众成翻译</a></p>
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<p>W3C中文资讯</p>
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<p>国外问答文章。类似于知乎。在上面提问题，有可能大牛会回答哦！</p>
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<li><p><a href="http://html5weekly.com/" target="_blank" rel="external">http://html5weekly.com/</a></p>
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ES规范转型之双等和全等
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2016-06-26
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<h1 id="关于双等"><a href="#关于双等" class="headerlink" title="关于双等"></a>关于双等</h1><p> 在比较双等时，javascript使用的是<code>抽象相等比较算法</code></p>
<p> 算法描述：</p>
<blockquote>
<p>比较运算x==y，其中x和y是值，产生true或者false。这样的比较按如下方式进行：</p>
<pre><code> 1. 若Type(x)与Type(y)相等，则
a. 若Type(x)为Undefined，则返回true。
b. 若Type(x)为Null，则返回true。
c. 若Type(x)为Number，则
i. 若x为NaN，返回false。
ii. 若y为NaN，返回false。
iii. 若x与y为相等数值，则返回true。
iv. 若x为+0，y为-0，返回true。
v. 若x为-0，y为+0，返回true。
vi. 返回false。
d. 若Type(x)为String，则当x和y为完全相等的字符序列（长度相等且相同字符出现在同样位置）时返回true。否则，返回false。
e. 若Type(x)为Boolean，则当x和y同为true或者同为false返回true。否则，返回false。
f. 若Type(x)为Object，则当x和y引用同一个对象时返回true。否则返回false。
2. 若x为null且y为undefined，返回true。
3. 若x为undefined且y为null，返回true。
4. 若Type(x)为Number且Type(y)为String，返回comparison x == ToNumber(y)的结果。
5. 若Type(x)为String且Type(y)为Number，
6. 返回toNumber(x) == y的结果。
7. 若Type(x)为Boolean，返回比较ToNumber(x) == y的结果。
8. 若Type(y)为Boolean，返回比较 x == ToNumber(y)的结果。
8. 若Type(x)为Object且Type(y)为String或Number，返回比较ToPrimitive(x) == y的结果。
10. 返回false。
</code></pre></blockquote>
<p>从规范的定义可知<code>抽象相等比较算法</code>有时候会递归调用。</p>
<p>例如true == “abc”：<br> true == “abc”，根据<code>7</code>，把true转为1，即<br> 1 == “abc”，然后再根据<code>4</code>，比较 1 == ToNumber(“abc”)，即<br> 1 == NaN，然后根据<code>1.c.ii</code>，最终返回false</p>
<p>例如true == “1”：<br> true == “1”，根据<code>7</code>，把true转为1，即<br> 1 == “1”，然后在根据<code>4</code>，比较 1 == ToNumber(“1”)，即<br> 1 == 1，然后根据<code>1.c.iii</code>，最终返回true</p>
<h1 id="关于全等"><a href="#关于全等" class="headerlink" title="关于全等"></a>关于全等</h1><p> 在比较全等时，javascript使用的是<code>严格相等比较算法</code></p>
<p> 算法描述：</p>
<blockquote>
<p>比较x===y，x和y为值，需要产出true或false。比较过程如下：</p>
<ol>
<li>若Type(x)与Type(y)的结果不一致，返回false，否则</li>
<li>如果Type(x)为Undefined，返回true</li>
<li>如果Type(x)为Null，返回true</li>
<li>如果Type(x)为Number，则<br>a. 如果x为NaN，返回false<br>b. 如果y为NaN，返回false<br>c. 如果x和y为同一个数字，返回true<br>d. 如果x为+0，y为-0，返回true<br>e. 如果x为-0，y为+0，返回true<br>f. 返回false<ol>
<li>如果Type(x)为String，如果x与y为完全相同的字符序列（相同长度和相同的字符对应相同的位置），返回true，否则，返回false</li>
<li>如果Type(x)为Boolean，如果x与y都为true或false，则返回true，否则，返回false</li>
<li>如果x和y引用同一个Obejct对象，返回true，否则，返回false</li>
</ol>
</li>
</ol>
</blockquote>
<p> 从算法描述上可知，全等是双等的一种情况，对应的是双等的<code>1</code></p>
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<a class="post-title-link" href="/2016/06/09/对DOM的修改永远都是异步的/" itemprop="url">
对DOM的修改永远都是异步的
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<time itemprop="dateCreated" datetime="2016-06-09T11:14:26+00:00" content="2016-06-09">
2016-06-09
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<h1 id="对DOM的修改永远都是异步的"><a href="#对DOM的修改永远都是异步的" class="headerlink" title="对DOM的修改永远都是异步的"></a>对DOM的修改永远都是异步的</h1><h1 id="这篇文章是错误的观点！"><a href="#这篇文章是错误的观点！" class="headerlink" title="这篇文章是错误的观点！"></a>这篇文章是错误的观点！</h1><p>例如下面的一个场景：</p>
<p>在页面上有2个script标签，第一个script标签内动态创建了一个script，去加载一个config.js文件，<br>第二个script标签内，需要用到动态加载的config</p>
<blockquote>
<p>config.js</p>
</blockquote>
<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></pre></td><td class="code"><pre><span class="line"><span class="built_in">window</span>.config = {</span><br><span class="line"> app:<span class="string">"调调"</span>,</span><br><span class="line"> version:<span class="string">"1.1.2"</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<blockquote>
<p>index.html</p>
</blockquote>
<figure class="highlight"><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">// 第一个script</span><br><span class="line"><script></span><br><span class="line"> (function(){</span><br><span class="line"> var script = document.createElement('script');</span><br><span class="line"> script.src = "config.js";</span><br><span class="line"> document.head.appendChild(script);</span><br><span class="line"> })()</span><br><span class="line"></script></span><br><span class="line"></span><br><span class="line">// 第二个script</span><br><span class="line"><script></span><br><span class="line"> (function(){</span><br><span class="line"> var config = window.config;</span><br><span class="line"> console.log(config); // undefined</span><br><span class="line"> })()</span><br><span class="line"></script></span><br></pre></td></tr></table></figure>
<p>出现上面问题的原因在于：</p>
<p><strong>对dom的修改永远都是异步的</strong></p>
<p>也就是说要等到所有已经加载的脚本执行完毕，再去修改DOM，然后加载并执行新的脚本</p>
<p>要根治这个问题，可以才用成熟的模块加载器如<code>RequireJS</code>,<code>SeaJS</code></p>
<h3 id="写了一段代码进一步验证-对dom的修改永远都是异步的"><a href="#写了一段代码进一步验证-对dom的修改永远都是异步的" class="headerlink" title="写了一段代码进一步验证 对dom的修改永远都是异步的"></a>写了一段代码进一步验证 对dom的修改永远都是异步的</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></pre></td><td class="code"><pre><span class="line"><span class="meta"><!DOCTYPE html></span></span><br><span class="line"><span class="tag"><<span class="name">html</span>></span></span><br><span class="line"><span class="tag"><<span class="name">head</span>></span></span><br><span class="line"><span class="tag"><<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"UTF-8"</span>></span></span><br><span class="line"><span class="tag"><<span class="name">title</span>></span>dom异步<span class="tag"></<span class="name">title</span>></span></span><br><span class="line"><span class="tag"></<span class="name">head</span>></span></span><br><span class="line"><span class="tag"><<span class="name">body</span>></span></span><br><span class="line"><span class="tag"><<span class="name">div</span> <span class="attr">id</span>=<span class="string">"d"</span>></span>默认文本<span class="tag"></<span class="name">div</span>></span></span><br><span class="line"><span class="tag"><<span class="name">script</span>></span><span class="javascript"></span><br><span class="line">d.onclick = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="keyword">this</span>.innerHTML = <span class="string">"往div里添加的新文本"</span>;<span class="comment">//更改一个节点</span></span><br><span class="line"> <span class="built_in">document</span>.body.appendChild(<span class="built_in">document</span>.createElement(<span class="string">"input"</span>));<span class="comment">//插入一个节点</span></span><br><span class="line"> <span class="keyword">for</span>(<span class="keyword">var</span> i = <span class="number">0</span>;i<<span class="number">10000000000</span>;i++);</span><br><span class="line">}</span><br><span class="line"></span><span class="tag"></<span class="name">script</span>></span></span><br><span class="line"><span class="tag"></<span class="name">body</span>></span></span><br><span class="line"><span class="tag"></<span class="name">html</span>></span></span><br></pre></td></tr></table></figure>
<p>原先的理解是：js修改dom是同步的，执行很快，但是渲染线程跟js引擎线程是互斥的，由于下面还有js代码要执行<br>所以渲染线程得不到机会来渲染新的修改后的dom。</p>
<p>原先理解的问题：没有考虑到有些dom是不需要渲染的，只存在于dom树中，例如head内的标签。所以如果修改了一个不需要渲染的标签，其表现也是异步的，那么就可以得出结论<strong>对dom的修改永远都是异步的</strong></p>
<p>现在的理解：js修改dom是异步的，下面的代码执行完毕，然后再来更新dom树，这些都完毕之后，渲染线程才得到机会来渲染新的修改后的dom</p>
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Promise用法总结
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<h1 id="一、断链执行"><a href="#一、断链执行" class="headerlink" title="一、断链执行"></a>一、断链执行</h1><p>比如下面的场景：</p>
<p>程序大部分的调用链是这样的：<code>promise.then(A).then(B).then(C).then(D)</code><br>但是B满足某种条件，需要这样调用：<code>promise.then(A).then(B).then(C1).then(C2).then(D)</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></pre></td><td class="code"><pre><span class="line">promise.then(A).then(B).then(<span class="function"><span class="keyword">function</span> (<span class="params">state</span>) </span>{</span><br><span class="line"> <span class="keyword">if</span> (state) {<span class="comment">//state可以来自B或A。但对于本次场景state来源与B</span></span><br><span class="line"> <span class="keyword">return</span> C();</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">return</span> C1().then(C2);</span><br><span class="line"> }</span><br><span class="line">}).then(D);</span><br></pre></td></tr></table></figure>
<h1 id="二、直接使用"><a href="#二、直接使用" class="headerlink" title="二、直接使用"></a>二、直接使用</h1><h3 id="1-使用new"><a href="#1-使用new" class="headerlink" title="1.使用new"></a>1.使用new</h3><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></pre></td><td class="code"><pre><span class="line"><span class="comment">/*</span><br><span class="line"> 这段代码中的resolve(999),会让这个promise对象立即进入resolved状态，并将</span><br><span class="line"> 999传递给后面then里所指定的resolve函数</span><br><span class="line"> 参数名不一定非要用resolve，也可以使用其他合法标识符，例如success</span><br><span class="line">*/</span></span><br><span class="line"><span class="keyword">var</span> promise = <span class="keyword">new</span> <span class="built_in">Promise</span>(<span class="function"><span class="keyword">function</span>(<span class="params"><span class="comment">/* success */</span> resolve</span>)</span>{</span><br><span class="line"> <span class="comment">// success(999);</span></span><br><span class="line"> resolve(<span class="number">999</span>);</span><br><span class="line">})</span><br><span class="line">promise.then( value => <span class="built_in">console</span>.log(value));</span><br></pre></td></tr></table></figure>
<h3 id="2-简写方式"><a href="#2-简写方式" class="headerlink" title="2.简写方式"></a>2.简写方式</h3><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 这段代码跟使用new方式是一样的。是上面的简写方式</span></span><br><span class="line"><span class="built_in">Promise</span>.resolve(<span class="number">999</span>).then(value => <span class="built_in">console</span>.log(value));</span><br></pre></td></tr></table></figure>
<p>直接使用这种方式，主要用于，后面可能有一系列能被（或者需要被）链式调用的操作，他们也需要一个Promise作为起始点<br>比如说，有两个有依赖的异步操作，<code>getUserById</code>和<code>getPostDetailByPostId</code>，此时<code>userId</code>已经有值<code>999</code>，<br>所以获取<code>userId</code>就不用异步，那后两个可以被链式调用的操作就不能和第一步链起来写了，很不爽。</p>
<p>所以可以使用<em>直接使用</em>的方式来写：</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></pre></td><td class="code"><pre><span class="line"><span class="built_in">Promise</span>.resolve(<span class="number">999</span>)</span><br><span class="line"> .then(userId => getUserById(userId))</span><br><span class="line"> .then(user => getPostDetailByPostId(user.postId))</span><br><span class="line"> .then(post => <span class="built_in">console</span>.log(post))</span><br></pre></td></tr></table></figure>
<p>使用这种写法的好处：</p>
<ul>
<li>表达因果关系</li>
<li>开发API时对外接口的一致性。例如大多数API都是异步的，现在突然冒出一个数据其实可以同步获取，但对外仍然提供一个统一的异步Promise返回更恰当</li>
</ul>
<p>当然，下面的写法也是可行的：</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></pre></td><td class="code"><pre><span class="line">getUserById(userId)</span><br><span class="line"> .then(user => getPostDetailByPostId(user.postId))</span><br><span class="line"> .then(post => <span class="built_in">console</span>.log(post));</span><br></pre></td></tr></table></figure>
<h1 id="三、最常用的使用方法"><a href="#三、最常用的使用方法" class="headerlink" title="三、最常用的使用方法"></a>三、最常用的使用方法</h1><p>用Promise包裹一个异步过程，并把这个Promise对象返回出去，以便在外部可以用then链式调用</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></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> getData = <span class="function"><span class="keyword">function</span>(<span class="params">data</span>)</span>{</span><br><span class="line"> </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"> <span class="keyword">try</span>{</span><br><span class="line"> <span class="comment">// .. </span></span><br><span class="line"> <span class="keyword">if</span>(data.state !== <span class="string">"SUCCESS"</span>){</span><br><span class="line"> reject(data);</span><br><span class="line"> }<span class="keyword">else</span>{</span><br><span class="line"> resolve(data);</span><br><span class="line"> }</span><br><span class="line"> }<span class="keyword">catch</span>(e){</span><br><span class="line"> reject(e);</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><br><span class="line"><span class="comment">// 第一种写法（推荐）</span></span><br><span class="line">getData()</span><br><span class="line"> .then(data => <span class="built_in">console</span>.log(data))</span><br><span class="line"> .catch(e => <span class="built_in">console</span>.log(e));</span><br><span class="line"></span><br><span class="line"><span class="comment">// 第二种写法</span></span><br><span class="line">getData().then(data => <span class="built_in">console</span>.log(data),e => <span class="built_in">console</span>.log(e));</span><br></pre></td></tr></table></figure>
<h1 id="四、多个Promise对象执行（循环中使用Promise）"><a href="#四、多个Promise对象执行（循环中使用Promise）" class="headerlink" title="四、多个Promise对象执行（循环中使用Promise）"></a>四、多个Promise对象执行（循环中使用Promise）</h1><h3 id="1-并行执行"><a href="#1-并行执行" class="headerlink" title="1.并行执行"></a>1.并行执行</h3><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> userIds = [<span class="number">111</span>,<span class="number">222</span>,<span class="number">333</span>];</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> promises = userIds.map( userId => getUserById(userId) );</span><br><span class="line"></span><br><span class="line"><span class="built_in">Promise</span></span><br><span class="line"> .all(promises)</span><br><span class="line"> .then(users => <span class="built_in">console</span>.log(users)); <span class="comment">// users就是根据ID列表得到的user列表</span></span><br></pre></td></tr></table></figure>
<h3 id="2-串行执行"><a href="#2-串行执行" class="headerlink" title="2.串行执行"></a>2.串行执行</h3><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> functions = [...];</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> promise = functions.raduce(<span class="function"><span class="keyword">function</span>(<span class="params">now,fn</span>)</span>{</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> now.then(fn);</span><br><span class="line"></span><br><span class="line"> },<span class="built_in">Promise</span>.resolve());</span><br><span class="line"></span><br><span class="line">promise.then(result => <span class="built_in">console</span>.log(result));</span><br></pre></td></tr></table></figure>
<h1 id="五、then链"><a href="#五、then链" class="headerlink" title="五、then链"></a>五、then链</h1><p><code>then(fn())</code> 与 <code>then(fn)</code> 的区别在于<br><code>then(fn())</code> 立即执行<code>fn</code>，<br><code>then(fn)</code> 异步执行<code>fn</code>，此时 <code>then(fn)</code>就是then链中不可或缺的一环了。</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">// 开启第一个异步任务，拿到所有SID</span></span><br><span class="line">getData({url:<span class="string">"v1/getalllist"</span>})</span><br><span class="line"> .then(<span class="function"><span class="keyword">function</span>(<span class="params">result</span>)</span>{</span><br><span class="line"> <span class="comment">// 处理第一个异步任务的结果</span></span><br><span class="line"> <span class="comment">// 开启第二个异步任务</span></span><br><span class="line"> <span class="keyword">return</span> getData({</span><br><span class="line"> url:<span class="string">"v1/getfullsku"</span>,</span><br><span class="line"> data:<span class="built_in">JSON</span>.stringify({</span><br><span class="line"> sids:<span class="built_in">Object</span>.keys(result) <span class="comment">//根据拿到的sid，再次拿全量SKU数据</span></span><br><span class="line"> })</span><br><span class="line"> });</span><br><span class="line"> })</span><br><span class="line"> .then(<span class="function"><span class="keyword">function</span>(<span class="params">result</span>)</span>{</span><br><span class="line"> <span class="comment">// 处理第二个异步任务的结果</span></span><br><span class="line"> <span class="comment">// do something ...</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">getData</span>(<span class="params">options</span>)</span>{</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"> $.ajax({</span><br><span class="line"> url:options.url,</span><br><span class="line"> data:options.data,</span><br><span class="line"> success:<span class="function"><span class="keyword">function</span>(<span class="params">result</span>)</span>{resolve(result);},</span><br><span class="line"> error:<span class="function"><span class="keyword">function</span>(<span class="params">e</span>)</span>{reject(e);}});</span><br><span class="line"> })</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>下面往then链上添加环节：</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></pre></td><td class="code"><pre><span class="line">getData({url:<span class="string">"v1/getalllist"</span>})</span><br><span class="line"> .then(<span class="built_in">console</span>.log(<span class="string">"getalllist done !!"</span>))</span><br><span class="line"> .then(<span class="function"><span class="keyword">function</span>(<span class="params">result</span>)</span>{</span><br><span class="line"> <span class="comment">// 处理第一个异步任务的结果</span></span><br><span class="line"> <span class="comment">// 开启第二个异步任务</span></span><br><span class="line"> <span class="keyword">return</span> getData({</span><br><span class="line"> url:<span class="string">"v1/getfullsku"</span>,</span><br><span class="line"> data:<span class="built_in">JSON</span>.stringify({</span><br><span class="line"> sids:<span class="built_in">Object</span>.keys(result) <span class="comment">//根据拿到的sid，再次拿全量SKU数据</span></span><br><span class="line"> })</span><br><span class="line"> });</span><br><span class="line"> })</span><br><span class="line"> .then(<span class="built_in">console</span>.log(<span class="string">"getfullsku done !!"</span>))</span><br><span class="line"> .then(<span class="function"><span class="keyword">function</span>(<span class="params">result</span>)</span>{</span><br><span class="line"> <span class="comment">// 处理第二个异步任务的结果</span></span><br><span class="line"> <span class="comment">// do something ...</span></span><br><span class="line"> })</span><br></pre></td></tr></table></figure>
<blockquote>
<p>结果是：马上打印了<code>getalllist done !!</code>和<code>getfullsku done !!</code>，并不会在接口调用完毕之后才执行相应的打印语句</p>
</blockquote>
<p>再次往then链上添加环节：</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">timer</span>(<span class="params"></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="built_in">console</span>.log(<span class="string">"timer function execute"</span>);</span><br><span class="line"> },<span class="number">2000</span>)</span><br><span class="line">}</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">timer2</span>(<span class="params">result</span>)</span>{</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="built_in">console</span>.log(<span class="string">"timer2 function execute"</span>);</span><br><span class="line"> resolve(result);</span><br><span class="line"> },<span class="number">2000</span>)</span><br><span class="line"> })</span><br><span class="line">}</span><br><span class="line">getData({url:<span class="string">"v1/getalllist"</span>})</span><br><span class="line"> .then(timer())</span><br><span class="line"> .then(timer) <span class="comment">// 报错了，此时timer为then链上的不可或缺的一环，但是在timer中并没有返回任何数据</span></span><br><span class="line"> .then(timer2) <span class="comment">// 不会报错，timer2返回一个promise对象，并且传递了第一个任务返回的数据给下方的then</span></span><br><span class="line"> .then(<span class="built_in">console</span>.log(<span class="string">"getalllist done !!"</span>))</span><br><span class="line"> .then(<span class="function"><span class="keyword">function</span>(<span class="params">result</span>)</span>{</span><br><span class="line"> <span class="comment">// 处理第一个异步任务的结果</span></span><br><span class="line"> <span class="comment">// 开启第二个异步任务</span></span><br><span class="line"> <span class="keyword">return</span> getData({</span><br><span class="line"> url:<span class="string">"v1/getfullsku"</span>,</span><br><span class="line"> data:<span class="built_in">JSON</span>.stringify({</span><br><span class="line"> sids:<span class="built_in">Object</span>.keys(result) <span class="comment">//根据拿到的sid，再次拿全量SKU数据</span></span><br><span class="line"> })</span><br><span class="line"> });</span><br><span class="line"> })</span><br><span class="line"> .then(<span class="built_in">console</span>.log(<span class="string">"getfullsku done !!"</span>))</span><br><span class="line"> .then(<span class="function"><span class="keyword">function</span>(<span class="params">result</span>)</span>{</span><br><span class="line"> <span class="comment">// 处理第二个异步任务的结果</span></span><br><span class="line"> <span class="comment">// do something ...</span></span><br><span class="line"> })</span><br></pre></td></tr></table></figure>
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nodejs中的模块
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<h1 id="模块的分类"><a href="#模块的分类" class="headerlink" title="模块的分类"></a>模块的分类</h1><ol>
<li>核心模块（http/fs/path…）</li>
<li>文件（本地）模块（自定义的js文件）</li>
<li>第三方模块（使用npm安装的第三方模块bluebird/cheerio/q…）</li>
</ol>
<p>在node里面文件和模块是一一对应的关系。</p>
<p>根据模块的类型有几种引入模块的方式，在nodejs里面可以通过文件路径来引用模块，也可以通过模块名来引用，如果使用模块名来引用非核心模块的话，node会把模块名映射到对应的模块文件的路径上。那些包含了核心函数的核心模块会在nodejs启动是被预先加载。</p>
<h1 id="node中关于模块的操作分为4个步骤"><a href="#node中关于模块的操作分为4个步骤" class="headerlink" title="node中关于模块的操作分为4个步骤"></a>node中关于模块的操作分为4个步骤</h1><ol>
<li>定义模块</li>
<li>导出模块</li>
<li>加载（引入）模块</li>
<li>使用模块</li>
</ol>
<h3 id="定义模块"><a href="#定义模块" class="headerlink" title="定义模块"></a>定义模块</h3><p>一个模块就是一个文件，例如<code>Person.class.js</code>，<code>Student.class.js</code></p>
<h3 id="导出模块"><a href="#导出模块" class="headerlink" title="导出模块"></a>导出模块</h3><p>导出模块的2种方式</p>
<p>第一种方式：</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="comment">// Person.class.js</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Person</span>(<span class="params">name.age</span>)</span>{</span><br><span class="line"> <span class="keyword">this</span>.name = name;</span><br><span class="line"> <span class="keyword">this</span>.age = age;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">Person.prototype.sayName = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="built_in">console</span>.log(\<span class="string">`My name is <span class="subst">${this.name}</span>\`);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">Person.prototype.sayAge = function(){</span><br><span class="line"> console.log(\`My age is <span class="subst">${this.age}</span>\`);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">module.exports = Person;</span></span><br></pre></td></tr></table></figure>
<p>第二种方式：</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// Student.class.js</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Student</span>(<span class="params">name,age,num</span>)</span>{</span><br><span class="line"> <span class="keyword">this</span>.name = name;</span><br><span class="line"> <span class="keyword">this</span>.age = age;</span><br><span class="line"> <span class="keyword">this</span>.num = num; <span class="comment">// 学号</span></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">Student.prototype.sayName = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="built_in">console</span>.log(\<span class="string">`My name is <span class="subst">${this.name}</span>\`);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">Student.prototype.sayAge = function(){</span><br><span class="line"> console.log(\`My age is <span class="subst">${this.age}</span>\`);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">Student.prototype.sayNum = function(){</span><br><span class="line"> console.log(\`My student number is <span class="subst">${this.num}</span>\`);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">exports.Student = Student;</span></span><br></pre></td></tr></table></figure>
<h3 id="使用模块"><a href="#使用模块" class="headerlink" title="使用模块"></a>使用模块</h3><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></pre></td><td class="code"><pre><span class="line"><span class="comment">// app.js</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> Person = <span class="built_in">require</span>(<span class="string">"./Person.class"</span>);</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> stuModule = <span class="built_in">require</span>(<span class="string">"./Student.class"</span>);</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> p = <span class="keyword">new</span> Person(<span class="string">"李彦峰"</span>,<span class="number">26</span>);</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> stu = <span class="keyword">new</span> stuModule.Student(<span class="string">"李彦峰"</span>,<span class="number">26</span>,<span class="number">455322185</span>);</span><br><span class="line"></span><br><span class="line">p.sayName(); <span class="comment">// My name is 李彦峰</span></span><br><span class="line"></span><br><span class="line">stu.sayNum(); <span class="comment">// My student number is 455322185</span></span><br></pre></td></tr></table></figure>
<p>两种导出模块的方式的区别是：<code>module.exports = Student</code>，在引入模块时，定义的接收变量就相当于<code>Student</code>；<br><code>exports.Student = Student</code>，在引入模块时，定义的接收变量相当于<code>exports</code>对象，要想使用，就必须用<code>接收变量.Student</code>才可以。</p>
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linux中的压缩与解压缩
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<p>linux中常用的压缩格式</p>
<ul>
<li>.zip</li>
<li>.gz</li>
<li>.bz2</li>
<li>.tar.gz</li>
<li>.tar.bz2</li>
</ul>
<p>下列所有的压缩命令和打包命令，如果压缩文件和打包文件前面有路径，就压缩或打包到指定的路径下<br>如果路径不存在就报错。</p>
<p>压缩率：.tar.bz2 > .tar.gz > .zip</p>
<h3 id="zip格式"><a href="#zip格式" class="headerlink" title=".zip格式"></a>.zip格式</h3><p>压缩命令为：zip 压缩文件名 源文件</p>
<p>例如：</p>
<ol>
<li>压缩文件 zip test.zip test.txt</li>
<li>压缩目录 zip -r test.zip test/</li>
<li>压缩多个文件 zip test.zuo 1.txt 2.txt</li>
<li>压缩多个目录 zip -r test.zip d1 d2</li>
<li>压缩多个目录和文件 zip -r test.zip d1 test.txt</li>
</ol>
<blockquote>
<p>可操作所有目录下的文件，在前面加上绝对或相对路径即可</p>
</blockquote>
<p>解压缩命令为：unzip 压缩文件名</p>
<p>例如：</p>
<ol>
<li>普通解压命令 unzip test.zip </li>
<li>解压到指定目录 unzip test.zip -d /tmp/</li>
<li>解压到指定目录没有就创建一个 unzip test.zip -d /tmp/test</li>
<li>查看压缩包内容 unzip -v test.zip</li>
</ol>
<h3 id="gz格式"><a href="#gz格式" class="headerlink" title=".gz格式"></a>.gz格式</h3><p>压缩命令为：gzip 源文件</p>
<p>压缩为.gz格式的压缩文件，源文件会消失。</p>
<p>gzip -c 源文件 > 压缩文件<br>如： gzip -c test.txt > text.gz<br>压缩为.gz格式的压缩文件，源文件保留。<br>没有一个像bz2一样的选项可以保留源文件，只能用这种比较trick的方式</p>
<p>gzip -r 目录<br>压缩目录下所有的子文件，但是不能压缩目录本身。</p>
<p>解压缩命令为：</p>
<p>1.gzip -d 压缩文件</p>