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<h1 id="this"><a class="header" href="#this">this</a></h1>
<p>解析器在调用函数每次都会向函数内部传递进一个隐含的参数，这个隐含的参数就是 this，this 指向的是一个对象，这个对象我们称为函数执行的 上下文对象。</p>
<h2 id="函数内-this-的指向非常重要"><a class="header" href="#函数内-this-的指向非常重要">函数内 this 的指向【非常重要】</a></h2>
<p>我们在《JavaScript 基础/函数.md》这篇文章讲过，函数的调用有<strong>六种</strong>形式。
根据函数的调用方式的不同，this 会指向不同的对象：</p>
<ul>
<li>1.以函数的形式（包括普通函数、定时器函数、立即执行函数）调用时，this 的指向永远都是
window。比如<code>fun();</code>相当于<code>window.fun();</code></li>
<li>2.以方法的形式调用时，this 指向调用方法的那个对象</li>
<li>3.以构造函数的形式调用时，this 指向实例对象</li>
<li>4.以事件绑定函数的形式调用时，this 指向<strong>绑定事件的对象</strong></li>
<li>5.使用 call 和 apply 调用时，this 指向指定的那个对象
<strong>针对第 1 条的举例</strong>：</li>
</ul>
<pre><code class="language-javascript">function fun() {
console.log(this);
console.log(this.name);
}
var obj1 = {
name: &quot;smyh&quot;,
sayName: fun,
};
var obj2 = {
name: &quot;vae&quot;,
sayName: fun,
};
var name = &quot;全局的name属性&quot;;
//以函数形式调用，this是window
fun(); //可以理解成 window.fun()
</code></pre>
<p>打印结果：</p>
<pre><code>Window
全局的name属性
</code></pre>
<p>上面的举例可以看出，this 指向的是 window 对象，所以 this.name 指的是全局的 name。
<strong>第 2 条的举例</strong>：</p>
<pre><code class="language-javascript">function fun() {
console.log(this);
console.log(this.name);
}
var obj1 = {
name: &quot;smyh&quot;,
sayName: fun,
};
var obj2 = {
name: &quot;vae&quot;,
sayName: fun,
};
var name = &quot;全局的name属性&quot;;
//以方法的形式调用，this是调用方法的对象
obj2.sayName();
</code></pre>
<p>打印结果：</p>
<pre><code>Object
vae
</code></pre>
<p>上面的举例可以看出，this 指向的是 对象 obj2 ，所以 this.name 指的是 obj2.name。</p>
<h3 id="箭头函数中-this-的指向"><a class="header" href="#箭头函数中-this-的指向">箭头函数中 this 的指向</a></h3>
<p>ES6 中的箭头函数并不会使用上面的准则，而是会继承外层函数调用的 this 绑定（无论 this 绑定到什么）。</p>
<h3 id="改变函数内部的-this-指向"><a class="header" href="#改变函数内部的-this-指向">改变函数内部的 this 指向</a></h3>
<p>JS 专门为我们提供了一些方法来改变函数内部的 this 指向。详见下一篇文章中的 call()、apply()、bind() 方法。</p>
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