编辑代码

function a(str) {
    let o = {};
    for (let i = 0; i < str.length; i++) {
        let chars= str.charAt(i);
        if (o[chars]) {
            o[chars]++;
        } else {
            o[chars] = 1;
        }
    }
    let max = 0;
    let ch = '';
    for (let k in o) {
        if (o[k] > max) {
            max = o[k];
            ch = k;
        }
    }   
    return max + ' ' + ch;
}
let re = a('abcdeacedfaacaa');
console.log(re);