JS 找出字符串中每个字符出现的次数且去重

1.找出每个字符出现的次数

let obj = {};
let arr = ['a','a','a','b','b','c','d','e','f','f'];
arr.map(x => obj[x]= obj[x] ? obj[x] + 1 : 1 );
console.log(obj);

2.字符去重，且，根据次数倒序显示

let orderObj = {}; 
Object.keys(obj).map(x=> { 
    if(orderObj[obj[x]] == undefined) orderObj[obj[x]] = [x]; 
    else orderObj[obj[x]].push(x);
})
Object.keys(orderObj).reverse().map(x => console.log(orderObj[x].join(' ')))