[Nexus]

<input type="number" id="answer"/>
<script>
var Game = (function() {
    let rightAnswer;

    return {
        generateNewRightValue: function() {
            rightAnswer = Math.floor(Math.random() * 31);

            return this;
        },
        check: function(answer) {
            return +answer == rightAnswer;
        }
    };
})().generateNewRightValue();

document.querySelector('#answer').addEventListener('input', function() {
    if (!Game.check(this.value))
        return void alert('Wrong');

    Game.generateNewRightValue();
    alert('Right');
});
</script>