隐式绑定

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<h1 id="h1_0" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 26px; font-stretch: normal; line-height: 40px; font-family: &quot;Microsoft YaHei&quot;, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">&nbsp; &nbsp; &nbsp;隐式绑定</h1><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;关于this，一般来说，谁调用了方法，该方法的this就指向谁，如：</p><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170728/1501205881690170.jpg" alt="1501205881690170.jpg"/></p><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);">如果存在多次调用，对象属性引用链只有上一层或者说最后一层在调用位置中起作用，如：</span></p><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170728/1501205914178101.jpg" alt="1501205914178101.jpg"/></p><h2 id="h2_1" style="border: 0px; margin: 0px 0px 20px; padding: 0px; font-size: 24px; font-stretch: normal; line-height: 36px; font-family: &quot;Microsoft YaHei&quot;, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;隐式丢失</h2><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;一个最常见的this绑定问题就是被<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">隐式绑定</code>的函数会丢失绑定对象，也就是说他回应用默认绑定，从而把this绑定到全局对象或者undefined上，取决于是否是严格模式。</p><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170728/1501205952974956.jpg" alt="1501205952974956.jpg"/></p><p></p><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;虽然bar是obj.foo的一个引用，但是实际上，它引用的是foo函数本身，因此此时的bar()其实是一个不带任何修饰的函数调用，因此应用了默认绑定</p><p style="border: 0px; margin-top: 0px; margin-bottom: 20px; padding: 0px; font-size: 15px; color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; white-space: normal; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;一个更微妙、更常见并且更出乎意料的情况发生在<code style="border: 0px; margin: 0px; padding: 0px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace;">传入回调函数时</code>：</p><p style="text-align: center"><img src="/Public/forum/ueditor/image/20170728/1501205977812056.jpg" alt="1501205977812056.jpg"/></p><p><span style="color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<code style="border: 0px; margin: 0px; padding: 0px; font-size: 15px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">参数传递其实就是一种隐式赋值</code><span style="color: rgb(46, 46, 46); font-family: &quot;Microsoft YaHei&quot;, 宋体, &quot;Myriad Pro&quot;, Lato, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgb(255, 255, 255);">，因此我们传入函数时也会被隐式赋值，所以结果和上一个例子一样，如果把函数传入语言内置的函数而不是传入自己声明的函数（如setTimeout等），</span><code style="border: 0px; margin: 0px; padding: 0px; font-size: 15px; font-family: Monaco, Consolas, &quot;Andale Mono&quot;, &quot;DejaVu Sans Mono&quot;, monospace; color: rgb(46, 46, 46); white-space: normal; background-color: rgb(255, 255, 255);">结果也是一样的</code></span><br/></p>

论坛站务软件水平考试华为认证计算机等级PMP认证思科认证Photoshop3DMAX编程语言移动开发系统运维产品运营淘宝营销办公软件Ps修图云计算大数据摄影就业