Title rewritten as: "Regular expression that works when using the u flag, but not when using the v flag"

Question

I encountered the following console warning in this regex pattern:

^[a-zA-Z0-9 _.-] @[a-zA-Z0-9] \\.[a-zA-Z0- 9] $

Pattern attribute value ^[a-zA-Z0-9 _.-] @[a-zA-Z0-9] \.[a-zA-Z0-9] $ ; is valid with the RegExp u flag, but not with the v flag: Uncaught SyntaxError: Invalid regular expression: /^[a-zA- Z0-9 _.-] @[a-zA-Z0-9] \.[a-zA-Z0-9] $/v: There are Invalid character.

I can't see how to create a valid regex pattern to resolve this warning. Could anyone please explain the error and how to fix it?

Trying to look at the documentation but can't find how to make it work with the v flag.

Answer 1

The problem is that the newly introduced v flag imposes more restrictions on escaping rules. Since it allows subtraction and intersection of character classes, the literal - at the end of the character class cannot remain unescaped.

Therefore, if you use the u flag, there is no such restriction, and if you use the v flag, there is such a restriction. See.

console.log(/^[a-zA-Z0-9+_.-]+@[a-zA-Z0-9]+\.[a-zA-Z0-9]+$/u.test("myname@somesite.com"))
console.log(/^[a-zA-Z0-9+_.\-]+@[a-zA-Z0-9]+\.[a-zA-Z0-9]+$/v.test("myname@somesite.com"))