獲取一個字串中出現最多的字元和他的個數

function isMax (STR) {
let obj = {};
    let arr = [];
    for (let item of STR) {
        if (!obj[item]) {
            obj[item] = 1;
        } else {
          obj[item]++;
        };
    };
    Object.keys(obj).forEach((item, index) => {
      let res = {
        name: item,
        value: obj[item]
      };
      arr.push(res);
    });
    let sort = arr.sort((a, b) => {
      return b.value - a.value;
    });
    let maxNum = sort[0].value;
    let maxStr = sort[0].name;
    console.log(`最多的字元是${maxStr},他有${maxNum}個`);
}