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原型与原型链
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<time datetime="2018-02-23T02:36:29.000Z" itemprop="datePublished">2018-02-23</time>
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<a class="article-category-link" href="/categories/烂笔头/">烂笔头</a>
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<span class="post-count">本文共 381 字</span>
<span class="post-count">预计花费 1 分钟</span>
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<blockquote>
<p>彻底搞清“原型与原型链”</p>
</blockquote>
<a id="more"></a>
<h2 id="prototype"><a href="#prototype" class="headerlink" title="prototype"></a><code>prototype</code></h2><ul>
<li><p>每个 <strong><em>函数</em></strong> 都有一个 <code>prototype</code> 属性，属性指向的是构造函数的原型。</p>
</li>
<li><p><strong>原型：</strong> 每一个 Javascript 对象（除 null 外）在创建的时候就会与之关联另一个对象，这个对象就是原型。</p>
</li>
</ul>
<h2 id="proto"><a href="#proto" class="headerlink" title="__proto__"></a><code>__proto__</code></h2><p>每一个 Javascript 对象（除了 null）都具有这个属性， <strong>指向该对象的原型</strong>。</p>
<figure class="highlight js"><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="function"><span class="keyword">function</span> <span class="title">Person</span>(<span class="params"></span>) </span>{</span><br><span class="line"></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> person = <span class="keyword">new</span> Person();</span><br><span class="line"></span><br><span class="line">person.__proto__ === Person.prototype; <span class="comment">// true</span></span><br></pre></td></tr></table></figure>
<h2 id="constructor-NaN"><a href="#constructor-NaN" class="headerlink" title="constructor"></a>constructor</h2><p>这个属性只存在于原型之上，指向相关联的构造函数。例如 <code>Person === Person.prototype.constructor</code>。 </p>
<h2 id="实例与原型"><a href="#实例与原型" class="headerlink" title="实例与原型"></a>实例与原型</h2><p>当读取实例的属性时，如果找不到，就会查找与对象关联的原型中的属性，如果还查不到，就去找原型的原型，一直找到最顶层为止</p>
<h2 id="原型与原型"><a href="#原型与原型" class="headerlink" title="原型与原型"></a>原型与原型</h2><p>原型也是一个对象，既然是对象，我们就可以用最原始的方式创建它。</p>
<figure class="highlight js"><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="keyword">var</span> obj = <span class="keyword">new</span> <span class="built_in">Object</span>();</span><br><span class="line">obj.name = <span class="string">'Kevin'</span></span><br><span class="line"><span class="built_in">console</span>.log(obj.name) <span class="comment">// Kevin</span></span><br></pre></td></tr></table></figure>
<p>原型对象就是通过 Object 构造函数生成的。</p>
<h2 id="原型链"><a href="#原型链" class="headerlink" title="原型链"></a>原型链</h2><figure class="highlight js"><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>.prototype.__proto__ === <span class="literal">null</span> <span class="comment">// true</span></span><br></pre></td></tr></table></figure>
<blockquote>
<p>null 表示“没有对象”，即该处不应该有值。</p>
</blockquote>
<p><strong><em>由相互关联的原型组成的链状结构就是原型链</em></strong></p>
<blockquote>
<p>综上汇集成一张图表示</p>
</blockquote>
<p><img src="https://myblog-static.oss-cn-beijing.aliyuncs.com/post-imgs/%E5%8E%9F%E5%9E%8B%E4%B8%8E%E5%8E%9F%E5%9E%8B%E9%93%BE/1-1.jpeg?x-oss-process=style/blogImg-watermark" alt="prototype"></p>
<h2 id="补充"><a href="#补充" class="headerlink" title="补充"></a>补充</h2><p><code>__proto__</code> 是每个对象都有的属性，它指向对象的原型。绝大部分浏览器都支持这个非标准的方法，<strong>但是它并不存在与原型之中</strong>，调用它的效果如同 <code>Object.getPrototypeOf(obj)</code>。</p>
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<ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#prototype"><span class="nav-number">1.</span> <span class="nav-text">prototype</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#proto"><span class="nav-number">2.</span> <span class="nav-text">__proto__</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#constructor-NaN"><span class="nav-number">3.</span> <span class="nav-text">constructor</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#实例与原型"><span class="nav-number">4.</span> <span class="nav-text">实例与原型</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#原型与原型"><span class="nav-number">5.</span> <span class="nav-text">原型与原型</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#原型链"><span class="nav-number">6.</span> <span class="nav-text">原型链</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#补充"><span class="nav-number">7.</span> <span class="nav-text">补充</span></a></li></ol>
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