SOURCE

const findMaxStr = (str)=>{
    let arr = str.split('');
    let count = {};
    let maxCount = 0;
    let mostChar;
    for(let i = 0;i<arr.length;i++){
        let char = arr [i]
        if(count[char]!==undefined){
            count[char]++
        }else{
            count[char] = 1
        }
    }
    Object.keys(count).forEach(char=>{
        if(count[char]>maxCount){
            maxCount = count[char]
            mostChar = char
        }
    });
    return '出现频率最高的字符是：' + mostChar + '，出现次数为：' + maxCount
}
console.log(findMaxStr('hello world'))