1. <script>
    2.         function firststr(s) {
    3.             for (let i = 0; i < s.length; i++) {
    4.                 if (s.indexOf(s[i]) === s.lastIndexOf(s[i])) {
    5.                     console.log(i)
    6.                     return i
    7.                 }
    8.             }
    9.             console.log(-1)
    10.             return -1
    11.         }
    12.         var s = "leelcode"
    13.         firststr(s)
    14.     </script>