The flags g, i, and m seem to be well-known regex flags in JavaScript.
However, there are some lesser known useful flags. The "dotAll" s flag can be
used to include newlines in a . wildcard match. The unicode u flag can be
used to match instances of unicode characters in a string. The sticky y
flag[1] can be used to start a search at a different index of the string than 0.
RegExp instances also have getter methods that can tell you which flags are
enabled[2].
[1] javascript.info
[2]
MDN