为什么这段代码卡住了node.js - Javascript上的Bug？

Question

I'm trying to run this regex but it stuck my console. Why?

var str = "Шедевры православной музыки - 20 золотых православных песен";
str.match(/^(([\u00C0-\u1FFF\u2C00-\uD7FF]+[^a-z\u00C0-\u1FFF\u2C00-\uD7FF]*)+) [a-z]+[^\u00C0-\u1FFF\u2C00-\uD7FF]*$/i);

Answer 1

Your regex causes catastrophic backtracking (see a demo of your regex here ) due to (([\À-\῿\Ⰰ-\퟿]+[^az\À-\῿\Ⰰ-\퟿]*)+) part. As [^az\À-\῿\Ⰰ-\퟿]* can match zero characters, you basically have a classical (a+)+ -like pattern (cf: ([\À-\῿\Ⰰ-\퟿]+)+ ) that causes backtracking issue.

To get rid of it, you need to make sure the subpatterns are compulsory inside the grouping, and apply a * quantifier to the whole grouping:

^([\u00C0-\u1FFF\u2C00-\uD7FF]+(?:[^a-z\u00C0-\u1FFF\u2C00-\uD7FF]+[\u00C0-\u1‌​FFF\u2C00-\uD7FF]+)*) [a-z]+[^\u00C0-\u1FFF\u2C00-\uD7FF]*$

See regex demo

Here, [\À-\῿\Ⰰ-\퟿]+(?:[^az\À-\῿\Ⰰ-\퟿]+[\À-\\u1‌​FFF\Ⰰ-\퟿]+)* matches:

• [\À-\῿\Ⰰ-\퟿]+ - one or more character from [\À-\῿\Ⰰ-\퟿] ranges
• (?:[^az\À-\῿\Ⰰ-\퟿]+[\À-\\u1‌​FFF\Ⰰ-\퟿]+)* - zero or more sequences of:
  • [^az\À-\῿\Ⰰ-\퟿]+ - one or more characters other than those from the az\À-\῿\Ⰰ-\퟿ ranges
  • [\À-\\u1‌​FFF\Ⰰ-\퟿]+ - one or more characters from the \À-\\u1‌​FFF\Ⰰ-\퟿ ranges.