first non-repeating char in a string

var str = 'the quick brown fox jumps then quickly blow air'

var arr = []

for(let i=0; i<=str.length; i++) {
  if (arr[str[i]]) {
    arr[str[i]]++
  } else {
    arr[str[i]] = 1
  }
}

console.log(arr)

for(let i=0; i<= str.length -1; i++) {
  if(arr[str[i]] == 1) {
    console.log(str[i])
  }
}