JSFiddle - React, Tailwind, and code Playground

JavaScript

function recurrent(arr) {
        var count = {},
        highest = 0,
            ret = null;
        for (var i = 0; i < arr.length; i++) {
            var curr = arr[i];
            count[curr] = typeof count[curr] === "undefined" ? 1 : count[curr] + 1;
        }
        for (var name in count) {
            if (!count.hasOwnProperty(name)) continue;
            var currCount = count[name];
            if (currCount > highest) {
                highest = currCount;
                ret = name;
            }
        }
        return ret;
    }

var a = [0, 0, 0, 1, 1, 2, 3, 4, 5, 5, 5, 5, 5, 6];
console.log(recurrent(a)); // 5