Regex remove repeated characters from a string by javascript

Question

I have found a way to remove repeated characters from a string using regular expressions.

function RemoveDuplicates() {
    var str = "aaabbbccc";
    var filtered = str.replace(/[^\w\s]|(.)\1/gi, "");  
    alert(filtered);
}

Output: abc this is working fine.

But if str = "aaabbbccccabbbbcccccc" then output is abcabc. Is there any way to get only unique characters or remove all duplicates one? Please let me know if there is any way.

Answer 1

A lookahead like "this, followed by something and this":

var str = "aaabbbccccabbbbcccccc";
console.log(str.replace(/(.)(?=.*\1)/g, "")); // "abc"

Note that this preserves the last occurrence of each character:

var str = "aabbccxccbbaa";
console.log(str.replace(/(.)(?=.*\1)/g, "")); // "xcba"

Without regexes, preserving order:

var str = "aabbccxccbbaa";
console.log(str.split("").filter(function(x, n, s) {
  return s.indexOf(x) == n
}).join("")); // "abcx"