find duplicate letters in string javascript code example

Example 1: how to find repeated characters in a string in javascript

const getRepeatedChars = (str) => {
  const strArr = [...str].sort();
  const repeatedChars = [];
  for (let i = 0; i < strArr.length - 1; i++) {
      if (strArr[i] === strArr[i + 1]) repeatedChars.push(strArr[i]);
  }
  return [...new Set(repeatedChars)];
};

getRepeatedChars("aabbkdndiccoekdczufnrz"); // ["a", "b", "c", "d", "k", "n", "z"]

Example 2: duplicate characters in a string javascript

const text = 'abcda'.split('')
text.some( (v, i, a) => {
  return a.lastIndexOf(v) !== i
}) // true