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class="content-wrap"><div id="content" class="content"><div id="posts" class="posts-expand"><article class="post post-type-normal" itemscope itemtype="http://schema.org/Article"><div class="post-block"><link itemprop="mainEntityOfPage" href="https://www.jealyn.top/jsexer2-ans.html"><span hidden itemprop="author" itemscope itemtype="http://schema.org/Person"><meta itemprop="name" content="jealyn.wang"><meta itemprop="description" content="前端小白一枚"><meta itemprop="image" content="/images/avatar.png"></span><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="Jealyn的个人网站"></span><header class="post-header"><h2 class="post-title" itemprop="name headline">js练习题第2天 答案及解析</h2><div class="post-meta"><span class="post-time"><span class="post-meta-item-icon"><i class="fa fa-calendar-o"></i> </span><span class="post-meta-item-text"></span> <time title="创建于" itemprop="dateCreated datePublished" datetime="2019-03-04T14:23:49+08:00">2019-03-04 </time></span><span class="post-category"><span class="post-meta-divider">|</span> <span class="post-meta-item-icon"><i class="fa fa-folder-o"></i> </span><span class="post-meta-item-text"></span> <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/JS基础练习题/" itemprop="url" rel="index"><span itemprop="name">JS基础练习题</span> </a></span>， <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/JS基础练习题/答案及解析/" itemprop="url" rel="index"><span itemprop="name">答案及解析</span> </a></span></span><span class="post-meta-divider">|</span> <span class="page-pv"><i class="fa fa-eye"></i> 阅读数 <span class="busuanzi-value" id="busuanzi_value_page_pv"></span>次</span><div class="post-wordcount"><span class="post-meta-item-icon"><i class="fa fa-file-word-o"></i> </span><span class="post-meta-item-text">字数统计:</span> <span title="字数统计">677 字 </span><span class="post-meta-divider">|</span> <span class="post-meta-item-icon"><i class="fa fa-clock-o"></i> </span><span class="post-meta-item-text">阅读时长 ≈</span> <span title="阅读时长">2 分钟</span></div></div></header><div class="post-body" itemprop="articleBody"><blockquote><p>本篇文章是js基础练习题第二天的答案及解析部分，纯题目部分请移步<a href="/jsexer2.html" title="js基础练习题 第2天">js基础练习题 第2天</a></p></blockquote><a id="more"></a><h2 id="正文"><a href="#正文" class="headerlink" title="正文"></a>正文</h2><p>1.<br></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="keyword">var</span> exerOne = <span class="string">'test;</span></span><br></pre></td></tr></table></figure>则<code>exerOne</code> = __________。<div class="note info"><h3>答案：报错（<code>SyntaxError</code>）</h3></div><div class="note warning"><p>字符串test缺少了闭合的引号。</p></div><br>2.<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="keyword">var</span> exerTwo = <span class="number">52</span> / <span class="number">0</span>;</span><br></pre></td></tr></table></figure>则 <code>exerTwo</code> = __________，<code>typeof(exerTwo)</code> = __________。<div class="note info"><h3>答案：<code>Infinity</code>、<code>"number"</code></h3></div><div class="note warning"><p>在js中，大于0的数除0，结果为<code>Infinity</code>；0除0，结果为<code>NaN</code>；小于0的数除0，结果为<code>-Infinity</code>。</p></div><br>3.<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="keyword">var</span> exerThree = <span class="number">0</span> / <span class="number">0</span>;</span><br></pre></td></tr></table></figure>则<code>exerThree</code> = __________，<code>typeof(exerThree)</code> = __________。<div class="note info"><h3>答案：<code>NaN</code>、<code>"number"</code></h3></div><br>4.<br><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="keyword">var</span> exerFour = <span class="string">"-3.3E+2-5"</span>;</span><br></pre></td></tr></table></figure>则<code>Number(exerFour)</code> = __________，<code>parseFloat(exerFour)</code> = __________。<div class="note info"><h3>答案：<code>NaN</code>、<code>-330</code></h3></div><div class="note warning"><p>该串字符为科学计数法与减法的混合，化为一般表示方法为<code>-3.3 * 10^2 - 5</code>。遇到第二个减号时就不再执行，<code>Number()</code>直接返回<code>NaN</code>，而<code>parseFloat()</code>则返回的是前部分的执行结果即<code>-3.3 * 10^2</code>。</p></div><br>5.<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="keyword">var</span> exerFive_1 = <span class="number">5</span> / <span class="number">2</span>; </span><br><span class="line"><span class="keyword">var</span> exerFive_2 = <span class="string">" is float?"</span>;</span><br></pre></td></tr></table></figure>则<code>exerFive_1 + exerFive_2</code> = __________。<div class="note info"><h3>答案：”2.5 is float?”</h3></div><br>6.<code>0.1 + 0.2 == 0.3</code> 的返回值为__________，若结果为假，请设计一种方法，使结果准确。<div class="note info"><p></p><h3>答案：如下代码段所示：</h3><p></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></pre></td><td class="code"><pre><span class="line"><span class="comment">// 方法一：固定小数位数</span></span><br><span class="line">(<span class="number">0.1</span> + <span class="number">0.2</span>).toFixed(<span class="number">1</span>)</span><br><span class="line"></span><br><span class="line"><span class="comment">// 方法二：化整再除</span></span><br><span class="line">(<span class="number">0.1</span> * <span class="number">10</span> + <span class="number">0.2</span> * <span class="number">10</span>) / <span class="number">10</span> </span><br></pre></td></tr></table></figure></div><br>7.<br><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="keyword">var</span> exerSeven = <span class="string">"this is\" test string"</span>;</span><br></pre></td></tr></table></figure>则<code>exerSeven.slice(5, 8)</code>的返回值是__________。<br><div class="note info"><h3>答案：”is””</h3></div><div class="note warning"><p><code>\"</code>将被转义为<code>"</code>，<code>String.slice(b, e)</code>方法将截取从b索引开始，到e索引（不包括e）结束的子串。</p></div><br>8.下面哪些操作不会改变原始数组，而是返回一个新的数组__________。<br>A、<code>forEach()</code> B、<code>reverse()</code> C、<code>sort()</code> D、<code>slice()</code><br>E、<code>concat()</code> F、<code>splice（）</code> G、<code>join（）</code> H、<code>shift（）</code><br>I、<code>reduce（）</code> J、<code>copyWithin()</code> K、<code>pop()</code> L、<code>map()</code><div class="note info"><h3>答案：A、D、E、L</h3></div><div class="note warning"><p>数组方法总结：</p><table><thead><tr><th>方法</th><th>描述</th><th>是否改变原始数组</th></tr></thead><tbody><tr><td>join()</td><td>返回以指定分隔符分隔而成的字符串</td><td>否</td></tr><tr><td>push()、unshift()</td><td>返回修改后数组的长度</td><td>是</td></tr><tr><td>pop()、shift()</td><td>返回弹出的元素</td><td>是</td></tr><tr><td>sort()</td><td>返回经过排序后的数组</td><td>是</td></tr><tr><td>reverse()</td><td>返回经过反序后的数组</td><td>是</td></tr><tr><td>concat()</td><td>返回合并后的数组</td><td>否</td></tr><tr><td>slice()</td><td>返回截取的数组</td><td>否</td></tr><tr><td>splice()</td><td>返回删除的元素组成的一个数组</td><td>是</td></tr><tr><td>indexOf()、lastIndexOf()</td><td>返回指定项的索引值</td><td>否</td></tr><tr><td>map()</td><td>返回每次函数调用结果组成的数组</td><td>否</td></tr><tr><td>filter()</td><td>返回符合过滤条件的结果组成的数组</td><td>否</td></tr><tr><td>reduce()</td><td>返回迭代函数处理后的值</td><td>否</td></tr><tr><td>copyWithin()</td><td>将数组中指定位置的成员复制到本数组其他位置</td><td>是</td></tr></tbody></table></div><p></p><h2 id="说明"><a href="#说明" class="headerlink" title="说明"></a>说明</h2><ol><li>题目中出现的JS指的是采用ECMAScript 2015及之后标准的JavaScript</li></ol><ol start="2"><li><p>答案中，若有错误和需完善的地方，可在下方留言反馈哈~~</p></li><li><p>查看纯习题版，请点击<a href="/jsexer2.html" title="js基础练习题 第2天">js基础练习题 第2天</a></p></li></ol></div><div><div><div style="text-align:center;color:#ccc;font-size:14px;letter-spacing:.2rem">--本文结束 <i class="fa fa-heart"></i> 感谢阅读--</div></div></div><div><div style="padding:10px 0;margin:20px auto;width:90%;text-align:center"><div>创作十分不易，原创更应鼓励</div><button id="rewardButton" disable="enable" onclick='var e=document.getElementById("QR");"none"===e.style.display?e.style.display="block":e.style.display="none"'><span>打赏</span></button><div id="QR" style="display:none"><div id="wechat" style="display:inline-block"><img id="wechat_qr" src="/images/wechatpay.png" alt="jealyn.wang 微信支付"><p>微信支付</p></div><div id="alipay" style="display:inline-block"><img id="alipay_qr" src="/images/alipay.png" alt="jealyn.wang 支付宝"><p>支付宝</p></div></div></div></div><div><ul class="post-copyright"><li 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href="#undefined"><span class="nav-number">1.1.</span> <span class="nav-text">答案：报错（SyntaxError）</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.2.</span> <span class="nav-text">答案：Infinity、"number"</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.3.</span> <span class="nav-text">答案：NaN、"number"</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.4.</span> <span class="nav-text">答案：NaN、-330</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.5.</span> <span class="nav-text">答案：”2.5 is float?”</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.6.</span> <span class="nav-text">答案：如下代码段所示：</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.7.</span> <span class="nav-text">答案：”is””</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#undefined"><span class="nav-number">1.8.</span> <span class="nav-text">答案：A、D、E、L</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#说明"><span class="nav-number">2.</span> <span class="nav-text">说明</span></a></li></ol></div></div></section></div></aside></div></main><footer id="footer" class="footer"><div class="footer-inner"><div class="copyright">© <span itemprop="copyrightYear">2019</span> <span class="with-love"><i class="fa fa-user"></i> </span><span class="author" itemprop="copyrightHolder">jealyn.wang</span></div><div class="busuanzi-count"><script async src="https://busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script><span class="site-uv">访客数 <i class="fa fa-user"></i> <span class="busuanzi-value" id="busuanzi_value_site_uv"></span> 人 </span><span class="site-pv">浏览数 <i class="fa fa-eye"></i> 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