Answers for "find the first element which is not repeated in the string js"

first duplicate javascript

function firstDuplicate(a) {
    let data = [];
    
    for (dup of a) {
        if (data[dup]) {
            return dup
        } else {
            data[dup] = dup
        }
    }
    return -1
}

first repeated character in a string javascript

function firstRepeatingCharacter(str) {
  for (let i = 0; i < str.length; i++) {
    if (str.indexOf(str.charAt(i)) !== str.lastIndexOf(str.charAt(i))) {
      return str.charAt(i)
    }
  }
  return 'no results found'
}