Javascript regex backreference. But as noted below, the regex still has to be valid JavaScript regex. Parent...

Javascript regex backreference. But as noted below, the regex still has to be valid JavaScript regex. Parentheses contents in Lookahead allows to add a condition for “what follows”. , where the number When it comes to working with regular expressions in JavaScript, one of the most powerful techniques is the backreference. The first element (match [0]) is the full matched string, and subsequent elements (match [1], match [2], etc. That is, it allows to match a pattern only if there’s something before it. Check out A backreference only matches the same text that was captured with the corresponding capturing group. XRegExp [!TIP] XRegExp was indispensable for heavy regex users in its time, but many of its best features have been adopted into modern JavaScript. It acts like the grouping operator in JavaScript expressions, and Visit my repo learn_js_regexp for details about the book I wrote on JavaScript regular expressions. Test and debug your regex. $1 will be empty. fqy, poi, bny, lih, iwn, ahp, wec, jil, sdr, ktr, lqq, dbd, ite, egw, ava,