How to convert a PCRE2 regex to JavaScript?

@Nils has the correct answer.

If you do need to expand your acceptable character set, you can use the following regex. Check it out. The g, m, and i flags are set.

(?<=hello ).*(?=\([^\)]*?\))

Hello Bob (Marius) Smith.
Hello Bob Jr. (Joseph) White
Hello Bob Jr. IInd (Paul) Jobs
Hello X Æ A-Xii (Not Elon) Musk
Hello Bob ()) Jr. ( (Darrell) Black

Match Number	Characters	Matched Text
Match 1	6-10	Bob
Match 2	32-40	Bob Jr.
Match 3	61-74	Bob Jr. IInd
Match 4	92-102	X Æ A-Xii
Match 5	124-138	Bob ()) Jr. (

The idea is pretty simple:

1. Look behind for your keyword: (?<=hello ).
2. Look ahead for your middle name: (?=\([^\)]*?\)) (anything inside a set of parenthesis that is not a closing parenthesis, lazily so you don't take part of the first name).
3. Take everything between as your first name: .*.

The ++ does not work as Javascript does not support possessive quantifiers.

As a first name, followed by a second name which is always between parens, you might also use a capture group with a match instead of a lookbehind.

\b[Hh]ello (\w+.*?)\s*\([^()\s]+\)

• \b[Hh]ello Match hello or Hello
• ( Capture group 1
  • \w.*? Match 1+ word chars followed by any char as least as possible
• ) Close group 1
• \s*\([^()\s]*\) Match optional whitespace char followed by ( till )

Regex demo

const regex = /\b[Hh]ello (\w+.*?)\s*\([^()\s]+\)/;
["Hello Bob (Marius) Smith.",
  "Hello Bob Jr. (Joseph) White",
  "Hello Bob Jr. IInd (Paul) Jobs"
].forEach(s => {
  const m = s.match(regex);
  if (m) {
    console.log(m[1]);
  }
})

With the lookbehind, you might also match word characters followed by an optionally repeated capture group matching whitspace chars followed by word characters or a dot.

(?<=[Hh]ello )\w+(?:\s+[\w.]+)*

Regex demo