How can I invert a regular expression in JavaScript?

Question

I have a string A and want to test if another string B is not part of it. This is a very simple regex whose result can be inverted afterwards.

I could do:

Answer 1

^(?!.*(word1|word2|word3))

will match a string that does not contain any of word1, word2, or word3 (and you can extend the list indefinitely). But this also matches null strings. To reject nulls use

^(?!$)(?!.*(word1|word2|word3))