Primes

<html>

<head>
    <title>Primes</title>
</head>

<script>
window.onload = function(){
    const form = document.body.querySelector('form');
    const input = form.querySelector('input');
    const submit = form.querySelector('input[type="submit"]');
    const time = document.body.querySelector('#tempo > span');
    const qnt = document.body.querySelector('#total > span');
    const result = document.body.querySelector('#result > span');

    form.addEventListener('submit', function(event){
        submit.setAttribute('disabled', 'disabled');
        event.preventDefault();
        result.innerText = '';

        const t0 = performance.now();

        const upTo = input.value;
        if (!upTo || upTo <= 1){
            submit.disabled = false;
            return;
        }

        var primes = [];

        for (let i=3; i <= upTo; i+=2){
            let isPrime = true;
            let root = Math.ceil(Math.sqrt(i))+1;
            for (let j=0; j < primes.length && primes[j] < root; j++){
                if (i%primes[j] == 0){
                    isPrime = false;
                    break;
                }
            }
            isPrime && primes.push(i);
        }
        primes.unshift(2);
        time.innerText = (performance.now() - t0) + " milliseconds.";
        qnt.innerText = primes.length;
        result.innerText = primes;
        submit.disabled = false;
    });
}
</script>

<body>

<form>
    <input type="text" value="20000">
    <input type="submit">
</form>

<div id="tempo">Tempo: <span></span></div>
<div id="total">Total: <span></span></div>
<div id="result" style="word-wrap: break-word">Resultado: <span></span></div>

</body>
</html>