Most regex implementations allow a lookbehind condition, so that such an expression:
(?<=hello )world
will match world only if it is preceded by hello. This functionality can prove useful at times, in particular when you can't or don't want to use capturing groups.
However, JavaScript notoriously doesn't offer this possibility. It allows lookahead, but not lookbehind.
My question concerns the rationale behind this "limitation".
- Is it purely technical? Perhaps the internals of
lookbehindwere considered too expensive for browsers by the time JavaScript regex implementation was designed - Is it because of political issues? Like with some other aspects of JavaScript who were not taken as far as they could have because of, say, Microsoft pushing back in the 2000's
- Is it purely deliberate? I heard many programmers saying they considered the use of
lookbehindas evil in most cases, so that it could have been skipped on purpose by this implementation's designers - Or perhaps, nobody really knows except the designers themselves?
EDIT: Not asking for guesses here. This question has been asked in the hope that somebody actually knows the answer.
