正则表达式错误:没什么可重复的 [英] Regex Error: Nothing to Repeat

问题描述

我不熟悉JavaScript中的正则表达式，因此无法使用正则表达式.错误是:

I'm new to regular expressions in JavaScript, and I cannot get a regex to work. The error is:

未捕获到的SyntaxError:无效的正则表达式:/(.* + x.* +)\ =(.++)/:无需重复

我知道除此以外还有很多这样的问题，但是我无法根据其他人的回答和建议来使它起作用.

I know there are many questions like this other than this, but I cannot get this to work based on other people's answers and suggestions.

正则表达式为:

/(.*+x.*+)\=(.++)/

，它用于在一侧将简单方程式与变量 x 匹配.

and it is used to match simple equations with the variable x on one side.

一些应该匹配的表达式示例(我正在编写一个简单的程序来求解变量 x ):

Some examples of the expressions it's supposed to match are (I'm writing a simple program to solve for the variable x):

• 240x = 70

x + 70 = 23

520/x = 2

13989203890189038902890389018930.23123213281903890128390x + 23123/2 = 3

等

我正在尝试所有格量词( * + )，因为以前，表达式很贪婪，导致浏览器崩溃，但是现在出现了我从未遇到的错误.

I'm trying out possessive quantifiers (*+) because before, the expressions were greedy and crashed my browser, but now this error that I haven't encountered has come up.

我确定这与转义无关，这是许多其他人的问题.

I'm sure it doesn't have to do with escaping, which was the problem for many other people.

推荐答案

您可以模拟所有量词与javascript(因为您可以模拟原子组一样)):

You can emulate a possessive quantifier with javascript (since you can emulate an atomic group that is the same thing):

a++ => (?>a+) => (?=(a+))\1

该技巧使用了这样的事实，即前瞻断言 (一旦正则表达式引擎达到右括号，?= ...)就变成原子的了.如果将捕获组放入其中(您希望是原子的或占有性的)，则只需添加

The trick use the fact that the content of a lookahead assertion (?=...) becomes atomic once the closing parenthesis reached by the regex engine. If you put a capturing group inside (with what you want to be atomic or possessive), you only need to add a backreference \1 to the capture group after.

关于您的图案:

.* + x 是一个总是错误的断言(例如.* + = ):由于.* 是贪婪的，因此它将匹配所有可能的字符，如果使它具有所有格.* + ，则正则表达式引擎无法回溯以匹配"x".

.*+x is an always false assertion (like .*+=): since .* is greedy, it will match all possible characters, if you make it possessive .*+, the regex engine can not backtrack to match the "x" after.

您可以做什么:

我建议不要使用含糊的.* ，而应更明确地描述可以包含每个捕获组的物质.我认为您不需要该任务的所有格修饰符.

Instead of using the vague .*, I suggest to describe more explicitly what can contain each capture group. I don't think you need possessive quantifiers for this task.

尝试在运算符上拆分字符串也是一个好主意，并且避免构建过于复杂的模式.

Trying to split the string on operator can be a good idea too, and avoids to build too complex patterns.

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