JS.09.02 Mid-level

Groups, lookarounds and Unicode + Regex safety and when not to use regex

Comes up in: JavaScript, Coding

This concept is being written. It gets the full five steps — explanation, predict, interview angle, practice with tests, and review cards. Here is exactly what it will cover, so you can study it elsewhere in the meantime.

What it covers

named groups
backreferences
lookahead/lookbehind
Unicode property escapes \p{L}
v flag set operations
lastIndex with g/y trap
catastrophic backtracking (ReDoS)
nested quantifiers
do not parse HTML/emails fully with regex
prefer URL, URLSearchParams, parsers

Words you will know

lookaheadlookbehindnamed groupUnicode property escapebacktrackingReDoS

What you will practise

parse log lines
password rules
find and fix a ReDoS pattern

Interview questions this answers

What is ReDoS and how do you avoid it?