Surprisingly short regex that matches valid JavaScript identifier names and captures it in a group according common JavaScript naming conventions, e.g:

myVariable generic name for most identifiers, uses camelCase

MyClass class names or names of other template-like items, uses UpperCamelCase or PascalCase

REGEX_101 global, user-defined (semantically) constant names, uses CAPS_CASE

101Regex doesn't match at all, JS names can't start with number

... etc. (see unit tests for more defs)