JSFiddle - React, Tailwind, and code Playground

JavaScript

function ArraySet () {
    this.s = [];
    this.m = 0;
    this.exist = function (o) {
        for (var i = 0; i < this.s.length; i++) {
            if (this.s[i] === o) {
                return true;
            }
        }
        return false;
    }
    this.max = function () {
        this.m = 0;
        for (var i = 0; i < this.s.length; i++) {
            if (this.s[i] > this.s[this.m]) {
                this.m = i;
            }
        }
		return this.m;
    }
    this.set = function (o) {
        if (!this.exist(o)) {
            if (this.s.length < 3) {
                this.s.push(o);
                return;
            }
            this.set = function (o) {
                if (!this.exist(o)) {
                    this.max();
                    if (o < this.s[this.m]) {
                        this.s[this.m] = o;
                    }
                }
            }
            this.set(o);
        }
        return;
    }
	this.getValue = function () {
		if (this.s.length < 3) {
			return false;
		}
		return this.s[this.max()];
	}
}

var ar = [1, 1, 1, 1, 2, 3];
var as = new ArraySet();
for (var i = 0; i < ar.length; i++)
    as.set(ar[i]);
alert(as.getValue());