SOURCE

// 查找字符串中出现最多的字符和个数
let str = 'a1aab2bbbccc3ccdddd4dd'

function strMax(str){
    let s = str.split('').sort().join('')
    console.log(s)
    let num = 0
    let char = ''
    s.replace(/(\w)\1+/g,($0, $1)=>{
        if($0.length > num){
            num = $0.length
            char = $1
        }
    })
    return `出现最多的字符是${char},出现了${num}次`
}

console.log(strMax(str))