获取javascript函数对象的参数个数（甚至名称） [英] Get argument count (or even names) of javascript function object

问题描述

我想在接受它之前评估回调函数。这意味着我需要知道至少接受的argumens的数量 - 如果count不匹配，我会在控制台中留下警告。
但是我找不到，javascript函数对象是否有一个属性可以帮助我获取这些信息。

因此，如果没有解析函数，就可以实现作为字符串（不值得）？

I want to evaluate callback function before accepting it. This means I need to know at least the count of accepted argumens - if count doesn't match, I'll leave warning in console. But I can't find out, whether a javascript function object has a property that would help me get that information.
So can this be achieved without parsing function as string (not worth it)?

推荐答案

一个函数有 a length 属性，它告诉你它接受多少个命名的参数。但是请注意，函数可以使用参数变量访问变量，即使它没有命名它们; 长度不适合这个（也没有替代方法）。

A function has a length property which tells you how many named arguments it accepts. Note however, a function can use the arguments variable to access variables, even if it doesn't name them; length doesn't cater for this (nor is there an alternative which does).

function foo(a, b) {
    for (var i=0;i<arguments.length;i++) {
        console.log(arguments[i]);
    }
}

console.log(foo.length); // reports 2, even though `foo` can access all your arguments!

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