Why does [\W_]+ with i modifier in Javascript regex match i,k,s?

Question

Forgot to remove the i modifier in a pattern, that should strip out non alphanumeric characters:

str.replace(/[\W_]+/gi," ");

And wondered, that [\W_] will match i,k and with + quantifier even s :D

Without the i modifier it's working fine. And of course the i modifier is a mistake, but I don't understand this weird behavior: regex101 and here is a fiddle

I'm using Firefox 32.0.1

Answer 1

It's a bug that affects Firefox 32.0 and 32.0.1.

It has already been fixed on Firefox 33 Beta.