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fa-bars fa-fw"></i></a></div></div></nav><div id="post-info"><h1 class="post-title">js数据类型和数据类型检测</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="2021-07-26T09:56:55.000Z" title="发表于 2021-07-26 17:56:55">2021-07-26</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="2022-08-05T08:51:19.295Z" title="更新于 2022-08-05 16:51:19">2022-08-05</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%89%8D%E7%AB%AF/">前端</a><i class="fas fa-angle-right post-meta-separator"></i><i class="fas fa-inbox fa-fw post-meta-icon"></i><a class="post-meta-categories" href="/categories/%E5%89%8D%E7%AB%AF/%E9%9D%A2%E8%AF%95%E9%A2%98/">面试题</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">713</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>2分钟</span></span><span class="post-meta-separator">|</span><span class="post-meta-pv-cv" id="" data-flag-title="js数据类型和数据类型检测"><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"><h2 id="js数据类型和数据类型检测"><a href="#js数据类型和数据类型检测" class="headerlink" title="js数据类型和数据类型检测"></a>js数据类型和数据类型检测</h2><h3 id="js数据类型"><a href="#js数据类型" class="headerlink" title="js数据类型"></a>js数据类型</h3><blockquote>
<ol>
<li>简单（基本）类型：String、Number、Boolean、Undefined、Null、Symbol</li>
<li>引用（复杂）类型：Object、Array、Function</li>
</ol>
</blockquote>
<h3 id="检测数据类型方法"><a href="#检测数据类型方法" class="headerlink" title="检测数据类型方法"></a>检测数据类型方法</h3><h4 id="typeof"><a href="#typeof" class="headerlink" title="typeof"></a><strong>typeof</strong></h4><blockquote>
<p> 一般用于检测基本数据类型，因为它检测引用（复杂）数据类型都会返回Objcet</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><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="variable language_">console</span>.<span class="title function_">log</span>(<span class="keyword">typeof</span> <span class="number">1</span>) <span class="comment">// number</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="keyword">typeof</span> <span class="string">'1'</span>) <span class="comment">// string</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="keyword">typeof</span> <span class="literal">undefined</span>) <span class="comment">// undefined</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="keyword">typeof</span> <span class="literal">true</span>) <span class="comment">// boolean</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="keyword">typeof</span> <span class="literal">null</span>) <span class="comment">// object</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">fun</span>(<span class="params"></span>){}</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="keyword">typeof</span> fun) <span class="comment">// function</span></span><br><span class="line"><span class="keyword">var</span> arr=[<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>,<span class="number">5</span>]</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="keyword">typeof</span> arr)<span class="comment">// object</span></span><br></pre></td></tr></table></figure>
<p>了解一下：typeof null返回值是object，因为js中的数据在底层是以二进制存储，如果前三位为0，那么就会判定为object，而null的所有都为0 ，所以null会被检测为object</p>
<h4 id="instanceof"><a href="#instanceof" class="headerlink" title="instanceof"></a><strong>instanceof</strong></h4><blockquote>
<p>instanceof是一个双目判断运算符，a instanceOf b ，用来检测构造函数的prototype属性是否出现在对象原型链中的任意位置，返回一个布尔值。</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><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">let</span> fun = <span class="keyword">function</span>(<span class="params"></span>){ }</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(fun <span class="keyword">instanceof</span> <span class="title class_">Function</span>) <span class="comment">//true</span></span><br><span class="line"><span class="keyword">let</span> obj ={ }</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(obj <span class="keyword">instanceof</span> <span class="title class_">Object</span>) <span class="comment">//true</span></span><br><span class="line"><span class="keyword">let</span> arr = [ ]</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr <span class="keyword">instanceof</span> <span class="title class_">Array</span>) <span class="comment">//true</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr <span class="keyword">instanceof</span> <span class="title class_">Object</span>) <span class="comment">//true</span></span><br></pre></td></tr></table></figure>
<p>这个方法主要是用来检测复杂数据类型的，不能用来检测基本数据类型，可以理解为用来检测构造函数的prototype属性是否出现在对象原型链中的任意位置，只要在当前实例的原型链上，我们用其检测出来的结果都是 true。在类的原型继承中，我们最后检测出来的结果未必准确。。</p>
<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="number">1</span> <span class="keyword">instanceof</span> <span class="title class_">Number</span> <span class="comment">//false </span></span><br><span class="line"><span class="literal">null</span> <span class="keyword">instanceof</span> <span class="title class_">Object</span> <span class="comment">// false</span></span><br></pre></td></tr></table></figure>
<p>instanceof运算符直接访问的变量的原始值，不会自动建立包装类。因此不能用来判断基本数据类型。</p>
<h4 id="constructor-NaN"><a href="#constructor-NaN" class="headerlink" title="constructor"></a><strong>constructor</strong></h4><blockquote>
<p><strong>语法：</strong>实例.constructor</p>
<p>对象的原型链下（构造函数的原型下）有一个属性，叫constructor, <strong>constructor 作用和 instanceof 非常相似。但 constructor 检测 Object 与 instanceof 不一样，还可以处理基本数据类型的检测。</strong></p>
<p>缺点：constructor并不可靠，因为它容易被修改。</p>
</blockquote>
<h4 id="Object-prototype-toString-call"><a href="#Object-prototype-toString-call" class="headerlink" title="Object.prototype.toString.call()"></a>Object.prototype.toString.call()</h4><blockquote>
<p>Object.prototype.toString.call()应该是目前最准确最常用的方式了，可以用来检测所有数据类型。在Object.prototype上有一个toString方法,这个方法执行的时候,会返回方法中this关键字对应数据值的数据类型,</p>
<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">//Object.prototype.toString() ->返回的是 Object.prototype 的数据类型 ->"[object Object]"</span></span><br><span class="line"><span class="comment">//f.toString() ->返回的是f的数据类型 ->"[object Object]"</span></span><br></pre></td></tr></table></figure>
<p>也就是，我想知道谁的所属类信息，我们就把这个toString方法执行，并且让this变为我们检测的这个数据值，那么方法返回的结果就是当前检测这个值得所属类信息 </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></pre></td><td class="code"><pre><span class="line"><span class="title class_">Object</span>.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">toString</span>.<span class="title function_">call</span>(<span class="number">12</span>)<span class="comment">//[boject Number]</span></span><br><span class="line"></span><br><span class="line"> <span class="title class_">Object</span>.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">toString</span>.<span class="title function_">call</span>(<span class="literal">true</span>)<span class="comment">//[boject Boolean]</span></span><br><span class="line"> <span class="comment">//"[object Number]"</span></span><br><span class="line"> <span class="comment">//"[object String]"</span></span><br><span class="line"> <span class="comment">//"[object Object]"</span></span><br><span class="line"> <span class="comment">//"[object Function]"</span></span><br><span class="line"> <span class="comment">//"[object Undefined]"</span></span><br><span class="line"> <span class="comment">//"[object Null]"</span></span><br><span class="line"> <span class="comment">//"[object RegExp]"</span></span><br><span class="line"> <span class="comment">//"[object Boolean]"</span></span><br><span class="line">......</span><br><span class="line"></span><br></pre></td></tr></table></figure>
</blockquote>
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