Get duplicate characters in string

Question

I try to match/get all repetitions in a string. This is what I\'ve done so far:

var str = \'abcabc123123\';
var REPEATED_CHARS_REGEX = /(.).*\\1/gi;

console         


        

Answer 1

Well, I think falsetru had a good idea with a zero-width look-ahead.

'abcabc123123'.match(/(.+)(?=\1)/g)
// ["abc", "123"]

This allows it to match just the initial substring while ensuring at least 1 repetition follows.

For M42's follow-up example, it could be modified with a .*? to allow for gaps between repetitions.

'abc123ab12'.match(/(.+)(?=.*?\1)/g)
// ["ab", "12"]

Then, to find where the repetition starts with multiple uses together, a quantifier ({n}) can be added for the capture group:

'abcabc1234abc'.match(/(.+){2}(?=.*?\1)/g)
// ["abcabc"]

Or, to match just the initial with a number of repetitions following, add the quantifier within the look-ahead.

'abc123ab12ab'.match(/(.+)(?=(.*?\1){2})/g)
// ["ab"]

It can also match a minimum number of repetitions with a range quantifier without a max -- {2,}

'abcd1234ab12cd34bcd234'.match(/(.+)(?=(.*?\1){2,})/g)
// ["b", "cd", "2", "34"]