什么是“！-"?用JavaScript做吗?

问题描述

我有这段代码(摘自这个问题):

I have this piece of code (taken from this question):

var walk = function(dir, done) {
    var results = [];

    fs.readdir(dir, function(err, list) {
        if (err)
            return done(err);

        var pending = list.length;

        if (!pending)
            return done(null, results);

        list.forEach(function(file) {
            file = path.resolve(dir, file);
            fs.stat(file, function(err, stat) {
                if (stat && stat.isDirectory()) {
                    walk(file, function(err, res) {
                        results = results.concat(res);

                        if (!--pending)
                            done(null, results);
                    });
                } else {
                    results.push(file);

                    if (!--pending)
                        done(null, results);
                }
            });
        });
    });
};

我正在尝试遵循它，我想我理解所有内容，除了结尾处显示！-pending 的内容.在这种情况下，该命令有什么作用?

I'm trying to follow it, and I think I understand everything except for near the end where it says !--pending. In this context, what does that command do?

感谢所有其他评论，但问题已得到多次解答.还是谢谢你！

I appreciate all the further comments, but the question has been answered many times. Thanks anyway!

推荐答案

！会反转一个值，并为您提供相反的布尔值:

! inverts a value, and gives you the opposite boolean:

!true == false
!false == true
!1 == false
!0 == true

-[value] 从一个数字中减去一(1)，然后返回该数字以供使用:

--[value] subtracts one (1) from a number, and then returns that number to be worked with:

var a = 1, b = 2;
--a == 0
--b == 1

因此，！-pending 从未决中减去1，然后返回其真实/虚假值的相反值(是否为 0 ).

So, !--pending subtracts one from pending, and then returns the opposite of its truthy/falsy value (whether or not it's 0).

pending = 2; !--pending == false
pending = 1; !--pending == true
pending = 0; !--pending == false

是的，请遵循ProTip.在其他编程语言中，这可能是常见的习惯用法，但是对于大多数声明性JavaScript编程而言，这似乎很陌生.

And yes, follow the ProTip. This may be a common idiom in other programming languages, but for most declarative JavaScript programming this looks quite alien.

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