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<h2 id="this-的指向"><a href="#this-的指向" class="headerlink" title="this 的指向"></a>this 的指向</h2><p><code>this</code> 是 js 中定义的关键字， 它的指向并不是在函数定义的时候确定的，而是在调用的时候确定的。换句话说，函数的调用方式决定了 this 指向。在实际应用中，<code>this</code>的指向大致可以分为以下四种情况。</p>
<blockquote>
<p>this的指向在函数定义的时候是确定不了的，只有函数执行的时候才能确定this到底指向谁(取决于函数的调用位置)，实际上this的最终指向的是那个调用它的对象(函数的直接调用者);</p>
</blockquote>
<hr>
<a id="more"></a>
<h3 id="作为普通函数调用-直接调用-：函数名"><a href="#作为普通函数调用-直接调用-：函数名" class="headerlink" title="作为普通函数调用(直接调用)：函数名()"></a>作为普通函数调用(直接调用)：函数名()</h3><p>当函数作为一个普通函数被调用，<code>this</code>指向全局对象。在浏览器里，全局对象就是 window。</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="built_in">window</span>.name = <span class="string">'cosyer'</span>;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">getName</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span>.name);</span><br><span class="line">}</span><br><span class="line">getName(); <span class="comment">// cosyer</span></span><br></pre></td></tr></table></figure>
<p>可以看出，此时<code>this</code>指向了全局对象 window。(NodeJS的全部对象是global)
在ECMAScript5的严格模式下，这种情况<code>this</code>已经被规定不会指向全局对象了，而是undefined。</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="meta">'use strict'</span>;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fun</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span>);</span><br><span class="line">}</span><br><span class="line">fun(); <span class="comment">// undefined</span></span><br></pre></td></tr></table></figure>
<h3 id="作为对象的方法调用"><a href="#作为对象的方法调用" class="headerlink" title="作为对象的方法调用"></a>作为对象的方法调用</h3><p>当函数作为一个对象里的方法被调用，<code>this</code>指向该对象</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="keyword">var</span> obj = {</span><br><span class="line"> name : <span class="string">'cosyer'</span>,</span><br><span class="line"> getName : <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span>.name);</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">obj.getName(); <span class="comment">// cosyer</span></span><br></pre></td></tr></table></figure>
<p>如果把对象的方法赋值给一个变量，再调用这个变量：</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></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> obj = {</span><br><span class="line"> fun1 : <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span>);</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"><span class="keyword">var</span> fun2 = obj.fun1;</span><br><span class="line">fun2(); <span class="comment">// window</span></span><br></pre></td></tr></table></figure>
<p>此时调用 fun2 方法 输出了 window 对象，说明此时<code>this</code>指向了全局对象。给 fun2 赋值，其实是相当于：</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="keyword">var</span> fun2 = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span>);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>可以看出，此时的<code>this</code>已经跟 obj 没有任何关系了。这时 fun2 是作为普通函数调用。</p>
<h3 id="作为构造函数调用"><a href="#作为构造函数调用" class="headerlink" title="作为构造函数调用"></a>作为构造函数调用</h3><p>js中没有类，但是可以从构造器中创建对象，并提供了<code>new</code>运算符来进行调用该构造器。构造器的外表跟普通函数一样，大部分的函数都可以当做构造器使用。当构造函数被调用时，<code>this</code>指向了该构造函数实例化出来的对象。</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="keyword">var</span> Person = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="keyword">this</span>.name = <span class="string">'cosyer'</span>;</span><br><span class="line">}</span><br><span class="line"><span class="keyword">var</span> obj = <span class="keyword">new</span> Person();</span><br><span class="line"><span class="built_in">console</span>.log(obj.name); <span class="comment">// cosyer</span></span><br></pre></td></tr></table></figure>
<p>如果构造函数显式的返回一个对象(function或者object)，那么<code>this</code>则会指向该对象。</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="keyword">var</span> Person = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="keyword">this</span>.name = <span class="string">'cosyer'</span>;</span><br><span class="line"> <span class="keyword">return</span> {</span><br><span class="line"> name : <span class="string">'chenyu'</span></span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"><span class="keyword">var</span> obj = <span class="keyword">new</span> Person();</span><br><span class="line"><span class="built_in">console</span>.log(obj.name); <span class="comment">// chenyu</span></span><br></pre></td></tr></table></figure>
<p>如果该函数不用<code>new</code>调用，当作普通函数执行，那么<code>this</code>依然指向全局对象。</p>
<h3 id="call-或-apply-调用-Function-prototype-bind-将当前函数绑定到指定对象绑定返回新函数之后再进行调用-间接调用、显示绑定"><a href="#call-或-apply-调用-Function-prototype-bind-将当前函数绑定到指定对象绑定返回新函数之后再进行调用-间接调用、显示绑定" class="headerlink" title="call() 或 apply() 调用 Function.prototype.bind()将当前函数绑定到指定对象绑定返回新函数之后再进行调用(间接调用、显示绑定)"></a>call() 或 apply() 调用 Function.prototype.bind()将当前函数绑定到指定对象绑定返回新函数之后再进行调用(间接调用、显示绑定)</h3><p>通过调用函数的 call() 或 apply() 方法可动态的改变<code>this</code>的指向。</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="keyword">var</span> obj1 = {</span><br><span class="line"> name : <span class="string">'cosyer'</span>,</span><br><span class="line"> getName : <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span>.name);</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"><span class="keyword">var</span> obj2 = {</span><br><span class="line"> name : <span class="string">'chenyu'</span></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">obj1.getName(); <span class="comment">// cosyer</span></span><br><span class="line">obj1.getName.call(obj2); <span class="comment">// chenyu</span></span><br><span class="line">obj1.getName.apply(obj2); <span class="comment">// chenyu</span></span><br></pre></td></tr></table></figure>
<p><strong>简单的实现bind方法</strong></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><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">const</span> obj = {};</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">test</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span> === obj);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="comment">// 自定义的函数，模拟 bind() 对 this 的影响</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">myBind</span>(<span class="params">func, target</span>) </span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="function"><span class="keyword">function</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="keyword">return</span> func.apply(target, <span class="built_in">arguments</span>); <span class="comment">// 第一个参数为函数运行的this指向</span></span><br><span class="line"> };</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> testObj = myBind(test, obj);</span><br><span class="line">test(); <span class="comment">// false</span></span><br><span class="line">testObj(); <span class="comment">// true</span></span><br></pre></td></tr></table></figure>
<p>从上面的示例可以看到，首先，通过闭包，保持了 target，即绑定的对象；然后在调用函数的时候，对原函数使用了 apply 方法来指定函数的 this。</p>
<p>不过使用 apply 和 call 的时候仍然需要注意，如果目录函数本身是一个绑定了 this 对象的函数，那 apply 和 call 不会像预期那样执行</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="keyword">const</span> obj = {};</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">test</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span> === obj);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="comment">// 绑定到一个新对象，而不是 obj</span></span><br><span class="line"><span class="keyword">const</span> testObj = test.bind({});</span><br><span class="line">test.apply(obj); <span class="comment">// true</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 期望 this 是 obj，即输出 true</span></span><br><span class="line"><span class="comment">// 但是因为 testObj 绑定了不是 obj 的对象，所以会输出 false</span></span><br><span class="line">testObj.apply(obj); <span class="comment">// false</span></span><br></pre></td></tr></table></figure>
<h2 id="一道this练习题"><a href="#一道this练习题" class="headerlink" title="一道this练习题"></a>一道this练习题</h2><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><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> length = <span class="number">10</span>;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params"></span>) </span>{</span><br><span class="line"> <span class="built_in">console</span>.log(<span class="keyword">this</span>.length)</span><br><span class="line">};</span><br><span class="line"><span class="keyword">var</span> obj = {</span><br><span class="line"> length: <span class="number">5</span>, </span><br><span class="line"> method: <span class="function"><span class="keyword">function</span> (<span class="params">fn</span>) </span>{</span><br><span class="line"> fn();</span><br><span class="line"> <span class="built_in">arguments</span>[<span class="number">0</span>](); <span class="comment">// this被绑定到arguments上，而arguments确实存在一个length属性，并且值为2</span></span><br><span class="line"> fn.call(obj, <span class="number">12</span>);</span><br><span class="line"> }</span><br><span class="line">};</span><br><span class="line">obj.method(fn, <span class="number">1</span>);</span><br><span class="line"><span class="comment">// 10 2 5</span></span><br></pre></td></tr></table></figure>
<ol>
<li>默认绑定</li>
<li>隐式绑定</li>
<li>显示绑定</li>
<li>new绑定<blockquote>
<p>默认绑定就是什么都匹配不到的情况下，非严格模式this绑定到全局对象window或者global,严格模式绑定到undefined;
隐式绑定就是函数作为对象的属性，通过对象属性的方式调用，这个时候this绑定到对象;
显示绑定就是通过bind、apply和call调用的方式;
new绑定就是通过new操作符时将this绑定到当前新创建的对象中</p>
</blockquote>
</li>
</ol>
<p>优先级： new>显示>隐式>默认</p>
<h2 id="箭头函数"><a href="#箭头函数" class="headerlink" title="箭头函数"></a>箭头函数</h2><div class="note info"><p>箭头函数的引入有两个方面的作用：一是更简短的函数书写，二是对<code>this</code>的词法解析。
在箭头函数出现之前，每个新定义的函数都有其自己的<code>this</code>值（例如，构造函数的<code>this</code>指向了一个新的对象；严格模式下的函数的<code>this</code>值为 undefined；如果函数是作为对象的方法被调用的，则其<code>this</code>指向了那个调用它的对象）。在面向对象风格的编程中，这会带来很多困扰。</p></div>
<h3 id="ES6-的箭头函数-gt-，指向与一般function定义的函数不同，比较容易绕晕，箭头函数this的定义：箭头函数中的this是在定义函数的时候绑定，而不是在执行函数的时候绑定。本质来说箭头函数没有自己的this，它的this是派生而来的。箭头函数会捕获其所在上下文的this值，作为自己的this值，即它会根据外层-函数或者全局-作用域继承-this-直接外层函数-。"><a href="#ES6-的箭头函数-gt-，指向与一般function定义的函数不同，比较容易绕晕，箭头函数this的定义：箭头函数中的this是在定义函数的时候绑定，而不是在执行函数的时候绑定。本质来说箭头函数没有自己的this，它的this是派生而来的。箭头函数会捕获其所在上下文的this值，作为自己的this值，即它会根据外层-函数或者全局-作用域继承-this-直接外层函数-。" class="headerlink" title="ES6 的箭头函数 ()=>，指向与一般function定义的函数不同，比较容易绕晕，箭头函数this的定义：箭头函数中的this是在定义函数的时候绑定，而不是在执行函数的时候绑定。本质来说箭头函数没有自己的this，它的this是派生而来的。箭头函数会捕获其所在上下文的this值，作为自己的this值，即它会根据外层(函数或者全局)作用域继承 this(直接外层函数)。"></a>ES6 的箭头函数 ()=>，指向与一般function定义的函数不同，比较容易绕晕，箭头函数<code>this</code>的定义：箭头函数中的<code>this</code>是在定义函数的时候绑定，而不是在执行函数的时候绑定。本质来说箭头函数没有自己的<code>this</code>，它的<code>this</code>是派生而来的。箭头函数会捕获其所在上下文的<code>this</code>值，作为自己的<code>this</code>值，即它会根据外层(函数或者全局)作用域继承 this(直接外层函数)。</h3><p>箭头函数将this指向其封闭的环境(也称“词法作用域”)。</p>
<h3 id="基础语法"><a href="#基础语法" class="headerlink" title="基础语法"></a>基础语法</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></pre></td><td class="code"><pre><span class="line"><span class="comment">// 等价于: => { return expression; } </span></span><br><span class="line">(param1, param2, …, paramN) => { statements }</span><br><span class="line">(param1, param2, …, paramN) => expression</span><br><span class="line"></span><br><span class="line"><span class="comment">// 如果只有一个参数，圆括号是可选的:</span></span><br><span class="line">(singleParam) => { statements }</span><br><span class="line">singleParam => { statements }</span><br><span class="line"></span><br><span class="line"><span class="comment">// 无参数或者多参数的箭头函数需要使用圆括号或者下划线:</span></span><br><span class="line">() => { statements } _ => { statements }</span><br></pre></td></tr></table></figure>
<h3 id="高级语法"><a href="#高级语法" class="headerlink" title="高级语法"></a>高级语法</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></pre></td><td class="code"><pre><span class="line"><span class="comment">// 只返回一个对象字面量,没有其他语句时, 应当用圆括号将其包起来:</span></span><br><span class="line">params => ({<span class="attr">foo</span>: bar})</span><br><span class="line"></span><br><span class="line"><span class="comment">// 支持 Rest parameters 和 default parameters:</span></span><br><span class="line">(param1, param2, ...rest) => { statements }</span><br><span class="line">(param1 = defaultValue1, param2, …, paramN = defaultValueN) => { statements }</span><br><span class="line"></span><br><span class="line"><span class="comment">// 支持参数列表中的解构赋值</span></span><br><span class="line"><span class="keyword">var</span> f = <span class="function">(<span class="params">[a, b] = [<span class="number">1</span>, <span class="number">2</span>], c=<span class="number">3</span> </span>) =></span> a + b + c;</span><br><span class="line">f(); <span class="comment">// 6</span></span><br></pre></td></tr></table></figure>
<h3 id="箭头函数不可以使用arguments对象，super或new-target"><a href="#箭头函数不可以使用arguments对象，super或new-target" class="headerlink" title="箭头函数不可以使用arguments对象，super或new.target"></a>箭头函数不可以使用arguments对象，super或new.target</h3><p>arguments对象在函数体内不存在，如果要用的话，可以用rest参数代替</p>
<h3 id="箭头函数没有原型"><a href="#箭头函数没有原型" class="headerlink" title="箭头函数没有原型"></a>箭头函数没有原型</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></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> Foo = <span class="function"><span class="params">()</span> =></span> {};</span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(Foo.prototype); <span class="comment">// undefined</span></span><br></pre></td></tr></table></figure>
<h3 id="箭头函数无法构造函数"><a href="#箭头函数无法构造函数" class="headerlink" title="箭头函数无法构造函数"></a>箭头函数无法构造函数</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></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> Foo = <span class="function"><span class="params">()</span> =></span> {};</span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> foo = <span class="keyword">new</span> Foo(); <span class="comment">// TypeError: Foo is not a constructor</span></span><br></pre></td></tr></table></figure>
<h3 id="箭头函数无法使用yield"><a href="#箭头函数无法使用yield" class="headerlink" title="箭头函数无法使用yield"></a>箭头函数无法使用yield</h3><p>yield 关键字通常不能在箭头函数中使用（除非是嵌套在允许使用的函数内）。因此，箭头函数不能用作生成器。</p>
<h3 id="箭头函数或者组件上绑定事件的时候this-xxx-bind-this-，这样会生成新函数，推荐constructor里bind-garbage-collection-垃圾回收机制-，除非使用purecomponent只进行浅比较。"><a href="#箭头函数或者组件上绑定事件的时候this-xxx-bind-this-，这样会生成新函数，推荐constructor里bind-garbage-collection-垃圾回收机制-，除非使用purecomponent只进行浅比较。" class="headerlink" title="箭头函数或者组件上绑定事件的时候this.xxx.bind(this)，这样会生成新函数，推荐constructor里bind() garbage collection(垃圾回收机制)，除非使用purecomponent只进行浅比较。"></a>箭头函数或者组件上绑定事件的时候this.xxx.bind(this)，这样会生成新函数，推荐constructor里bind() garbage collection(垃圾回收机制)，除非使用purecomponent只进行浅比较。</h3>
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<div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#this-的指向"><span class="nav-number">1.</span> <span class="nav-text">this 的指向</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#作为普通函数调用-直接调用-：函数名"><span class="nav-number">1.1.</span> <span class="nav-text">作为普通函数调用(直接调用)：函数名()</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#作为对象的方法调用"><span class="nav-number">1.2.</span> <span class="nav-text">作为对象的方法调用</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#作为构造函数调用"><span class="nav-number">1.3.</span> <span class="nav-text">作为构造函数调用</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#call-或-apply-调用-Function-prototype-bind-将当前函数绑定到指定对象绑定返回新函数之后再进行调用-间接调用、显示绑定"><span class="nav-number">1.4.</span> <span class="nav-text">call() 或 apply() 调用 Function.prototype.bind()将当前函数绑定到指定对象绑定返回新函数之后再进行调用(间接调用、显示绑定)</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#一道this练习题"><span class="nav-number">2.</span> <span class="nav-text">一道this练习题</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#箭头函数"><span class="nav-number">3.</span> <span class="nav-text">箭头函数</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#ES6-的箭头函数-gt-，指向与一般function定义的函数不同，比较容易绕晕，箭头函数this的定义：箭头函数中的this是在定义函数的时候绑定，而不是在执行函数的时候绑定。本质来说箭头函数没有自己的this，它的this是派生而来的。箭头函数会捕获其所在上下文的this值，作为自己的this值，即它会根据外层-函数或者全局-作用域继承-this-直接外层函数-。"><span class="nav-number">3.1.</span> <span class="nav-text">ES6 的箭头函数 ()=>，指向与一般function定义的函数不同，比较容易绕晕，箭头函数this的定义：箭头函数中的this是在定义函数的时候绑定，而不是在执行函数的时候绑定。本质来说箭头函数没有自己的this，它的this是派生而来的。箭头函数会捕获其所在上下文的this值，作为自己的this值，即它会根据外层(函数或者全局)作用域继承 this(直接外层函数)。</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#基础语法"><span class="nav-number">3.2.</span> <span class="nav-text">基础语法</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#高级语法"><span class="nav-number">3.3.</span> <span class="nav-text">高级语法</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#箭头函数不可以使用arguments对象，super或new-target"><span class="nav-number">3.4.</span> <span class="nav-text">箭头函数不可以使用arguments对象，super或new.target</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#箭头函数没有原型"><span class="nav-number">3.5.</span> <span class="nav-text">箭头函数没有原型</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#箭头函数无法构造函数"><span class="nav-number">3.6.</span> <span class="nav-text">箭头函数无法构造函数</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#箭头函数无法使用yield"><span class="nav-number">3.7.</span> <span class="nav-text">箭头函数无法使用yield</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#箭头函数或者组件上绑定事件的时候this-xxx-bind-this-，这样会生成新函数，推荐constructor里bind-garbage-collection-垃圾回收机制-，除非使用purecomponent只进行浅比较。"><span class="nav-number">3.8.</span> <span class="nav-text">箭头函数或者组件上绑定事件的时候this.xxx.bind(this)，这样会生成新函数，推荐constructor里bind() garbage collection(垃圾回收机制)，除非使用purecomponent只进行浅比较。</span></a></li></ol></li></ol></div>
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