JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = [3, 7, 7, 7, 7, 10, 10, 8, 5, 5, 5, 5, 20, 20, 1],
    result = {},
    max = 0,
    res, key, min;

for (var i = 0, total = arr.length; i < total; ++i) {
    var val = arr[i],
        inc = (result[val] || 0) + 1;

    result[val] = inc;

    if (inc > max) {
        max = inc;
        res = val;
    }
}
for (var i in result) {
    if (result[i] === max) {
        key = parseInt(i, 10);
        min = min || key;
        console.log(min)
        if (min > key) {
            min = key;

        }
    }
}
res = min;
alert(res);