JSFiddle - React, Tailwind, and code Playground

JavaScript

var array = ['75', '100', 'b', 'b', 'a', 'a'];
var mf = 1;
var m = 0;
var item;
for (var i=0; i<array.length; i++){
    for (var j=i; j<array.length; j++) {
        if (array[i] == array[j])
            m++;
        if (mf<m){
            mf=m; 
            item = array[i];
        }
     }
     m=0;
}
alert(item);