How to implement inverted string in javascript

var str = "abcdefg";                //常规方法使用for循环加charAt

                function reverse(str){

                    var result ="";                    for(var i = str.length; i > 0; i-- ){

                        console.log(str.charAt(i-1));

                        result +=  str.charAt(i-1);

                    }                    return result;

                }

//巧妙使用array的reverse和join方法

                function reverse(str){

                    var result, arr = str.split("");    //使用空字符则会直接分割字符返回数组[a,b,c,d,e,f,g]

                    var result = arr.reverse().join("");                    return result; 

                }

var op = document.querySelectorAll("select option");

                var arr = Array.prototype.slice.call(op,1);

                arr.forEach(function(item, index, arr){

                    item.style.backgroundColor = "red";

                    console.log(index);

                    console.log(item);

                    console.log(arr);

                });