Answers for "non repeating character in javascript"

first non repeating character javascript

function firstNotRepeatingCharacter(s) {
    for (let i = 0; i < s.length; i++) {
        if(s.indexOf(s.charAt(i)) == s.lastIndexOf(s.charAt(i))) {
            return s.charAt(i)
        }
    }
    return '_'    
}

duplicate characters in a string javascript

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