为什么if (!condition) {console.log(condition)}显示true [duplicate]

This question already has an answer here:

这个问题已经有了答案:

What is wrong with my date regex? [duplicate] 2 answers
我的约会regex怎么了?(重复)2的答案

I want to make a String method, which accepts a RegExp and a callback, then splits String by RegExp, and inserts callback's return in split array. In short, it would do something like this:

我想创建一个String方法，它接受RegExp和回调，然后通过RegExp分割字符串，并在分割数组中插入回调的返回。简而言之，它将做如下事情:

"a 1 b 2 c".method(/\d/, function ($1) { return $1 + 1; })
    => [a, 2, b, 3, c]

In case the String doesn't match the RegExp, it should return an array, like this:

如果字符串与RegExp不匹配，它应该返回一个数组，如下所示:

"a b c d e".method(/\d/, function ($1) { return $1 + 1; })
    => ["a b c d e"]

I wrote this code, but it doesn't work as I thought:

我写了这段代码，但它不像我想的那样:

String.prototype.preserveSplitReg = function(reg, func) {

    var rtn = [], 
        that = this.toString();
    if (!reg.test(that)) {
        console.log(reg, that, reg.test(that));
        return [that];
    }

    ...
}

The console.log should be called ONLY when the String doesn't match reg, right? But sometimes it logs (reg, that, true). That troublesome String and reg were:

控制台。只有当字符串不匹配reg时才调用日志，对吗?但有时它会记录(reg, that, true)那个麻烦的字符串和reg是:

"See <url>http://www.w3.org/TR/html5-diff/</url> for changed elements and attributes, as well as obsolete elements and"
/<url>.*?<\/url>/g

console logs true. I can't figure out why. Any help would be highly appreciated.

真正的控制台日志。我搞不懂为什么。如有任何帮助，我们将不胜感激。

1 个解决方案

#1

This is due to a bug in Javascript RegEx engine (ECMAScript3)

这是由于Javascript RegEx引擎(ECMAScript3)中的一个错误造成的。

Basically a regex with the g modifier doesn't reset correctly, so multiple test() calls toggle between true and false.

基本上，带有g修饰符的正则表达式不能正确重置，因此多个测试()调用在true和false之间进行切换。

See also this answer: https://*.com/a/3827500/548225 for more details.
详情请参见:https://*.com/a/3827500/548225。

#1