I'm trying to match: --This is a text and it <b>can contain other </b> tags--
I will wrap matched pattern with <u></u>
But i'm trying to avoid <br> tag only. I.e it shouldn't match if the string has <br> in between --
text.replace(/(?:--)(?:(?!--|\s))((?!<br>).*?)(?:--)/g,'<u>$1</u>')
Unfortunately, my regex matches
--This is a text, <b>can contain other</b>tags but don't match if <br> is present--
I don't expect it to match since <br> is present.
Make (?!<br>). as a group, then quantify this group, instead of quantifying . only. Aslo, ? is redundant after * because ? means 0 or 1 while * means 0 or more, which already cover 1.
(?:--)(?:(?!--|\s))((?:(?!<br>).)*)(?:--)
Bonus: You don't need capture group if you use positive look ahead and positive look behind for --, if your environment support it. This match itself will exclude the --.
(?<=--)(?:(?!--|\s))(?:(?!<br>).)*(?=--)
First check if string does not contain <br> and then continue regex:
if (!/--.*?<br>.*?--/.test(text)) {
text.replace(/(?:--)(?:(?!--|\s))((?!<br>).*?)(?:--)/g,'<u>$1</u>')
}