Groups and ranges indicate groups and ranges of expression characters. Non-capturing groups matches "x" and behaves like capturing groups, but it does not remember the match.
Keep in mind that capturing groups have a performance penalty. If you don't need the matched substring to be recalled, prefer non-capturing groups.
Write a RegEx that matches colors in the format #abc or #abcdef. That is: # followed by 3 or 6 hexadecimal digits. Use a non capturing group in your expression.
let REGEXP = /your regexp/g
let str = "color: #3f3; background-color: #AA00ef; and: #abcd"
str.match(REGEXP) ; ➞ #3f3 #AA00ef