let str = 'bkdaksfkjagjksfgkjasgfkjhaskjgf';

        let obj = {};

       //先将字符串遍历出来，并转化为对象        

   for (var i = 0; i < str.length; i++) {

            let arr = str.charAt(i);

            if (obj[arr]) {

                obj[arr]++;

            } else {

                obj[arr] = 1;

            };

        };

        console.log(obj);

        let maxobj = '';

        let maxnum = 1;

   / /遍历转化出来的对象

        for (let k in obj) {

            if (obj[k] > maxnum) {

                maxnum = obj[k];

                maxobj = k;

            }

        };

        let index = str.indexOf(maxobj);

        console.log(index);