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class="fa-fw fas fa-archive"></i><span> 归档</span></a></li><li><a class="site-page child" href="/about/"><i class="fa-fw fas fa-heart"></i><span> 关于</span></a></li><li><a class="site-page child" target="_blank" rel="noopener" href="https://buy.dreamlove.top/"><i class="fa-fw fas fa-heart"></i><span> 购物</span></a></li></ul></div></div><div id="toggle-menu"><a class="site-page" href="javascript:void(0);"><i class="fas fa-bars fa-fw"></i></a></div></div></nav><div id="post-info"><h1 class="post-title">今日刷题-原型链</h1><div id="post-meta"><div class="meta-firstline"><span class="post-meta-date"><i class="far fa-calendar-alt fa-fw post-meta-icon"></i><span class="post-meta-label">发表于</span><time class="post-meta-date-created" datetime="2022-05-07T08:37:40.000Z" title="发表于 2022-05-07 08:37:40">2022-05-07</time><span class="post-meta-separator">|</span><i class="fas fa-history fa-fw post-meta-icon"></i><span class="post-meta-label">更新于</span><time class="post-meta-date-updated" datetime="2022-05-07T08:37:00.000Z" title="更新于 2022-05-07 08:37:00">2022-05-07</time></span><span class="post-meta-categories"><span class="post-meta-separator">|</span><i class="fas fa-inbox fa-fw post-meta-icon"></i><a class="post-meta-categories" href="/categories/%E5%88%B7%E9%A2%98/">刷题</a></span></div><div class="meta-secondline"><span class="post-meta-separator">|</span><span class="post-meta-wordcount"><i class="far fa-file-word fa-fw post-meta-icon"></i><span class="post-meta-label">字数总计:</span><span class="word-count">386</span><span class="post-meta-separator">|</span><i class="far fa-clock fa-fw post-meta-icon"></i><span class="post-meta-label">阅读时长:</span><span>1分钟</span></span><span class="post-meta-separator">|</span><span class="post-meta-pv-cv" data-flag-title="今日刷题-原型链"><i class="far fa-eye fa-fw post-meta-icon"></i><span class="post-meta-label">阅读量:</span><span id="busuanzi_value_page_pv"><i class="fa-solid fa-spinner fa-spin"></i></span></span></div></div></div></header><main class="layout" id="content-inner"><div id="post"><article class="post-content" id="article-container"><h3 id="题目1"><a href="#题目1" class="headerlink" title="题目1"></a>题目1</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></pre></td><td class="code"><pre><span class="line">请问以下两次检测对象constructor是否拥有属性名<span class="number">1</span>的结果分别是什么？</span><br><span class="line"><span class="number">1</span> <span class="keyword">in</span> <span class="title class_">Object</span>(<span class="number">1.0</span>).<span class="property">constructor</span>;</span><br><span class="line"><span class="title class_">Number</span>[<span class="number">1</span>] = <span class="number">123</span>;</span><br><span class="line"><span class="number">1</span> <span class="keyword">in</span> <span class="title class_">Object</span>(<span class="number">1.0</span>).<span class="property">constructor</span>;</span><br><span class="line"></span><br><span class="line"><span class="attr">A</span>: <span class="literal">false</span>,<span class="literal">false</span></span><br><span class="line"></span><br><span class="line"><span class="attr">B</span>: <span class="literal">false</span>,<span class="literal">true</span></span><br><span class="line"></span><br><span class="line"><span class="attr">C</span>: <span class="literal">true</span>,<span class="literal">true</span></span><br><span class="line"></span><br><span class="line"><span class="attr">D</span>: <span class="literal">true</span>,<span class="literal">false</span></span><br></pre></td></tr></table></figure><ul><li><p>答案</p><ul><li>B</li></ul></li><li><p>解析</p><ul><li><p><code>in</code>用于检测一个属性是否在指定对象上或者是其原型链上</p></li><li><p><strong><code>Object</code> 构造函数将给定的值包装为一个新对象。</strong></p><ul><li>比如Object({name:’李白’}) 返回 { name : ‘李白’ }</li><li>Object([1,2,3,4]) 返回[1,2,3,4]</li><li>Object(1.0) 返回Number(1) 也就是Number对象</li></ul><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></pre></td><td class="code"><pre><span class="line"><span class="comment">// 代码等同于</span></span><br><span class="line"><span class="keyword">var</span> temp = <span class="title class_">Object</span>(<span class="number">1.0</span>);</span><br><span class="line"></span><br><span class="line"><span class="number">1</span> <span class="keyword">in</span> temp.<span class="property">constructor</span>;</span><br><span class="line"></span><br><span class="line"><span class="comment">//Object[key] = value; 形式给 constructor 对象添加 key = 1 属性,对应的 value = 123 </span></span><br><span class="line"><span class="comment">// 因为key不能为数字开头,所以就通过Ojbect[key]方式赋值</span></span><br><span class="line"><span class="comment">// 类似于 Object.name = "李白"这种</span></span><br><span class="line"><span class="title class_">Number</span>[<span class="number">1</span>] = <span class="number">123</span>;</span><br><span class="line"></span><br><span class="line"><span class="number">1</span> <span class="keyword">in</span> temp.<span class="property">constructor</span>;</span><br></pre></td></tr></table></figure></li></ul></li></ul><h3 id="题目2"><a href="#题目2" class="headerlink" title="题目2"></a>题目2</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></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> F=<span class="keyword">function</span>(<span class="params"></span>){};</span><br><span class="line"><span class="title class_">Object</span>.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">a</span>=<span class="keyword">function</span>(<span class="params"></span>){};</span><br><span class="line"><span class="title class_">Function</span>.<span class="property"><span class="keyword">prototype</span></span> .<span class="property">b</span>=<span class="keyword">function</span>(<span class="params"></span>){};</span><br><span class="line"><span class="keyword">var</span> f=<span class="keyword">new</span> <span class="title function_">F</span>();</span><br><span class="line"><span class="attr">A</span>: f能取到a，但取不到b</span><br><span class="line"></span><br><span class="line"><span class="attr">B</span>: f能取到a,b</span><br><span class="line"></span><br><span class="line"><span class="attr">C</span>: F能取到b，不能取到a</span><br><span class="line"></span><br><span class="line"><span class="attr">D</span>: F能取到a，不能取到b</span><br><span class="line"></span><br></pre></td></tr></table></figure><ul><li><p>答案</p><ul><li>A</li></ul></li><li><p>解析</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></pre></td><td class="code"><pre><span class="line"><span class="comment">// 看代码~</span></span><br><span class="line"><span class="keyword">var</span> F = <span class="keyword">function</span> (<span class="params"></span>) {};</span><br><span class="line"><span class="keyword">var</span> f = <span class="keyword">new</span> <span class="title function_">F</span>();</span><br><span class="line">F.<span class="property">__proto__</span> === <span class="title class_">Function</span>.<span class="property"><span class="keyword">prototype</span></span>; <span class="comment">//true</span></span><br><span class="line">f.<span class="property">__proto__</span> === F.<span class="property"><span class="keyword">prototype</span></span>; <span class="comment">//true</span></span><br><span class="line">F.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">__proto__</span> === <span class="title class_">Object</span>.<span class="property"><span class="keyword">prototype</span></span>; <span class="comment">//true</span></span><br><span class="line"></span><br><span class="line">F.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">__proto__</span> == <span class="title class_">Function</span>.<span class="property"><span class="keyword">prototype</span></span>; <span class="comment">//false</span></span><br></pre></td></tr></table></figure><p>图形演示</p><p><img src="https://dreamos.oss-cn-beijing.aliyuncs.com/gitblog/202205070910644.png" alt="原型链"></p></li></ul><h3 id="题目3"><a href="#题目3" class="headerlink" title="题目3"></a>题目3</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">下面哪些语句可以 在<span class="variable constant_">JS</span>里判断一个对象是否为<span class="title class_">String</span>类型？</span><br><span class="line"><span class="attr">A</span>: oStringObject <span class="keyword">instanceof</span> <span class="title class_">String</span></span><br><span class="line"></span><br><span class="line"><span class="attr">B</span>: <span class="keyword">typeof</span> oStringObject == <span class="string">'string'</span></span><br><span class="line"></span><br><span class="line"><span class="attr">C</span>: oStringObject is <span class="title class_">String</span> (没见过这个语法~)</span><br><span class="line"></span><br><span class="line"><span class="attr">D</span>: 以上答案都不正确</span><br><span class="line"></span><br></pre></td></tr></table></figure><ul><li><p>答案</p><ul><li>A</li></ul></li><li><p>解析</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"><span class="comment">//所以只有a</span></span><br><span class="line"><span class="keyword">typeof</span> <span class="string">'hello'</span>; <span class="comment">// 'string'</span></span><br><span class="line"><span class="keyword">typeof</span> <span class="keyword">new</span> <span class="title class_">String</span>(<span class="string">'hello'</span>); <span class="comment">// 'object'</span></span><br></pre></td></tr></table></figure></li></ul></article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta"><i class="fas fa-circle-user fa-fw"></i>文章作者: </span><span class="post-copyright-info"><a href="https://www.dreamlove.top">梦洁</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta"><i class="fas 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