07 实现strStr()

<script>
        function strStr(haystack, needle){
            if(needle == null){
                console.log(-1)
                return -1
            }else{
                if(haystack.includes(needle)){
                    console.log(haystack.indexOf(needle))
                    return haystack.indexOf(needle)
                }else{
                    console.log(-1)
                    return -1
                }
            }
        }
        var haystack="hello" 
        var needle = "ll"
        strStr(haystack, needle)
    </script>