否定字符 class 与带有 unicode 标志的 JavaScript RegExp 不匹配？

Question

/[^|]$/u.test('') returns true , but /\|[^|]$/u.test('|') returns false .

( is a Unicode SIP char ⷗4 that is represented as a surrogate pair ? in JavaScript.)

I expect that [^|] matches any single Unicode char except for a literal | and thus should match. For the same reason, \| plus [^|] should match | plus.

However the real world JavaScript obviously doesn't work as above (tested in Firefox 103 and Chromium 103). Can anyone explain why?

Answer 1

Without Unicode u flag combined with i flag (that would enable Unicode case folding ), the [^|] negated character class only matches what /[\0-\x7B\x7D-�]/ matches (see Unicode-aware regular expressions in ES2015 ), and as you see, this does not match astral plane chars.

If you can use ES6 you can use

 console.log( /\|[^|]$/ui.test("|") )

Answer 2

It appears to be a bug of the V8 JavaScript engine of Chromium according to the developers in the recent report and has been fixed which will be included in Chrome 106 onwards.

Firefox seems to implement its RegExp under some source code of V8, and will be waiting for the upstream fix. ( ref )