SOURCE

var arr="dgdgjdgkdgjdgkdgjdgkdgagdgdddddddddd";
var newArr=arr.split("");
var json={};
var numArr=[];
var lagStr=null;
var lagLen=null;

newArr.map((item,index)=>{
	json[item]=0;
});

Object.keys(json).map((item,index)=>{
	let b=new RegExp(item,"g");
	let c=arr.match(b);
	json[item]=c.length;
	numArr.push(c.length);
})
lagLen=Math.max(...numArr); // return large num
for(var item in json){

	if(json[item]==lagLen)lagStr=item;
}

console.log(lagLen)