The first kind of

var str = "aaasssksldnfkjr"
var o = {}
for (var i = 0; i < str.length; i++) {
    var name = str[i]
    if (o[name]) {
        o[name]++
    } else {
        o[name] = 1
    }
}
var max = 0;
var maxs = ""
for (var name in o) {
    if (max < o[name]) {
        max = o[name];
        maxs = name
    }
}
console.log(max, maxs)
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Second method of regularization

var str = "aaasssksldnfkjr"
var arr = str.split("")
var Arr = arr.sort()
var s = Arr.join("")
console.log(s)
var max = 0;
var maxs=""
s.replace(/(\w)\1+/g,function(s,s2){
    if(s.length>max){
        max=s.length;
        maxs=s2
    }
})
console.log(max, maxs) 
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The third kind of

var str = "aaasssksldnfkjr" var arr = str.split("") var Arr = arr.sort(); var max=0; var maxs=""; var n=1 for(var i=0; i<Arr.length; i++){ if(Arr[i]==Arr[i+1]){ n++ }else{ if(n>max){ max=n; maxs=Arr[i] } n=1 } } console.log(max, maxs)Copy the code