Javascript如何匹配回调函数中的参数？ [英] How does Javascript match the parameters in the callback function?

问题描述

我刚开始学习Javascript，回调函数似乎很难理解。我有一个问题是JavaScript如何匹配参数在回调函数？例如以下forEach循环：

I just started to learn Javascript, and callback functions seem hard to understand. One question I have is how javascript matches the parameters in a callback function? for example in the following forEach loop:

var friends = ['Mike', 'Stacy', 'Andy', 'Rick'];    
friends.forEach(function(eachName, index){
      console.log(index + 1 + ". " + eachName);
    });

默认情况下，forEach函数会将索引传递给第二个参数，并输入第一个参数在回调函数中？

Is it by default that the forEach function will pass index to the second parameter and entry to the first parameter in the callback function?

为了掌握回调函数，我需要在每次使用它时检查API（在这种情况下，forEach）吗？

In order to master callback functions, do I need to check the API (in this case, forEach) every time I use it?

推荐答案

默认情况下，forEach函数将通过索引到第二个参数和回调函数中的第一个参数的入口？

Is it by default that the forEach function will pass index to the second parameter and entry to the first parameter in the callback function?

是的; 这是规范的一部分。实际上，它还传递正在迭代的数组作为第三个参数。

Yes; this is part of the specification. In fact, it also passes the array being iterated as the third argument.

使用T调用callbackfn的[[Call]]内部方法作为包含[值]，[索引]和[对象] 的此值和参数列表。

Call the [[Call]] internal method of callbackfn with T as the this value and argument list containing [the value], [the index], and [the object].

（强调我的）

为了掌握回调函数，我需要检查API（在这种情况下， forEach）每次我使用它？

In order to master callback functions, do I need to check the API (in this case, forEach) every time I use it?

好吧，他们是相互一致的，所以你会记住在某一点。 map ，过滤器，每和一些也可以这种方式工作。

Well, they’re pretty consistent with each other, so you’ll remember at some point. map, filter, every, and some also work in this way.

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