为什么IIFE这个关键字指的是窗口对象..？ [英] Why IIFE this keyword refers to window object..?

问题描述

当我运行以下代码时，为什么IFFE 此引用窗口对象而不是 a

When I run the below code why the IFFE this refers to window object and not to a

var a = {
 printThis : function () {
 console.log('printThis', this);
  var inner = (function () {
    console.log('inner', this);
   })();
  }
};

a.printThis（）;

a.printThis();

//输出

printThis 一个对象

printThis a object

内部窗口对象< - 为什么..？

inner window object <-- why..?

推荐答案

请考虑以下示例：

var a = {};
var b = {};
a.hello = function() { console.log(this); };
b.hello = a.hello;

在大多数编程语言中， b.hello（）将打印 a ，因为它们基于这个来确定函数的位置。该函数在 a 中，所以此是 a 。有道理，对吗？

In most programming languages, b.hello() would print a since they base this on where the function is. The function is in a, so this is a. Makes sense, right?

然而，JavaScript在这方面有点不同。而不是它在哪里，它基于如何被称为。 b.hello（）在 b 上调用 hello ，从而此设置为 b 。这也是有道理的，因为JavaScript并没有真正具有where函数的概念（不像Java中的方法，它总是与特定的类绑定），并且很难确定 a 就是是。

However, JavaScript is a bit different in that regard. Instead of where it is, it's based on how it was called. b.hello() calls hello on b, thus this is set to b. This also makes sense since JavaScript doesn't really have a concept of "where" a function is (unlike methods in, say, Java, which are always tied to a specific class), and it's hard to determine that a is where it "is".

所以， foo.bar（）对于栏的调用，将始终将此设置为 foo c $ c>（除非有人使用 bind 或类似的事先将此绑定到特定值）。

So, foo.bar() will always set this to foo for the purposes of this call to bar (unless one has used bind or similar to bind this to a specific value in advance).

现在，一个IIFE被调用......没什么，真的。它不是 foo.bar（）的情况，它只是一个 bar（）其中 bar 是你的函数表达式。在这种情况下，没有 foo ，它默认为窗口对象。

Now, an IIFE is invoked on... nothing, really. It's not a foo.bar() situation, it's just a bar() where bar is your function expression. In cases like this where there's no foo, it defaults to the window object.

有两种简单的解决方法：

There are two simple workarounds:

1. 在IIFE之外创建一个包含您感兴趣的值的变量： var that = this; 并使用 代替此在IIFE中，或


2. bind 此值：（function（）{CODE GOES HERE}）。bind（this）（）;

1. Create a variable outside the IIFE containing the value you´re interested in: var that = this; and use that instead of this in the IIFE, or
2. bind the this value: (function(){ CODE GOES HERE }).bind(this)();

这篇关于为什么IIFE这个关键字指的是窗口对象..？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！