How could you find the first non repeating char in a string?

First non repeating char : First way

//First non repeating char :  How could you find the first non repeating char in a string?
function firstNonRepeatChar(s) {
  for (var i = 0; i < s.length; i++) {
    var letter = s.charAt(i);
    if (s.substring(s.indexOf(letter) + 1, s.length).indexOf(letter) == -1) {
      console.log(letter);
      break;
    }
  }
}

var text =  "the quick brown fox jumps then quickly blow air";
firstNonRepeatChar(text); 

First non repeating char : second way

//First non repeating char :  How could you find the first non repeating char in a string?
function firstNonRepeatChar1(s) {
  for (var i = 0; i < s.length; i++) {
    var letter = s.charAt(i); 
    if(s.lastIndexOf(letter) == s.indexOf(letter)){
      console.log(letter);
      break;
    }
  }
}

firstNonRepeatChar1('QQQQQ');