在回调函数中访问变量......什么？ [英] Accessing variable in callback function... what?

问题描述

我经历了大量的帖子，我终于得到了我需要的东西，这要归功于：

I've been through a ton of posts and I finally got what I needed thanks to this:

$("a.foo").click(function(){
    var that = this;
    jPrompt("Type something:","","", function(r) {
        $(that).text(r);
    }
}

来自以下：
在回调函数中访问$（this）

我想知道是否有人可以扩展这里到底发生了什么（为什么这个没有重新分配？ ）我应该阅读哪些核心信息？从我收集的内容中，这可能与封闭有关...这是我在搜索时遇到的大部分内容。这是准确的吗？

I was wondering if someone could expand on what exactly is happening here (why is this not available without re-assigning?) and what core information I should read up on? From what I gather this might have something to do with closures... that's most of what I bumped into while searching around. Is that accurate?

在我的情况下，我想要执行一些代码，然后在ajax请求完成后重定向。在回调函数中，我运行 $（this）.attr（href） 返回未定义。

In my case, I was looking to execute some code, then redirect once an ajax request completed. In the callback function I was running $(this).attr("href") which was returning undefined.

推荐答案

此根据函数的调用方式由javascript分配。因此， jPrompt（）函数确定在<$ c $> 中的值 c> jPrompt（）调用回调。

this is assigned by javascript according to how a function is called. So, it is the jPrompt() function that determines what value this will have in your callback when jPrompt() calls the callback.

所以，除非jPrompt通过你输入的一些参数来阻止这个的相同值，它可能会有不同的价值。因此，您可以将其保存，以便在回调中进行访问。这是javacscript回调中非常常见的设计模式。

So, unless jPrompt goes out of its way to keep the same value for this via some argument you passed in, it will likely have a different value. As such, you can save it away for access within the callback as you've done. This is a very common design pattern in javacscript callbacks.

仅供参考，分配了此的一些方法：

FYI, some of the ways that this is assigned:

• obj.method（） - this in 方法（）将设置为 obj


• func.call（obj） - 此 in func（）将设置为 obj


• func（） - 此将在 func（）或<$中设置为窗口 c $ c>未定义严格模式

• obj.method() - this in method() will be set to obj
• func.call(obj) - this in func() will be set to obj
• func() - this will be set to window in func() or undefined in strict mode

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