How to get a date with JavaScript and insert it into a hidden form input?

Question:

I need javascript to automatically fill in an <input type="hidden" /> with the current date, and another with 15 days after the current date.

It will be used for the date of issue of a bank slip and the other for the expiration date of the bank slip, and I need the format to be aaaammdd .

<input name="dataEmissao" type="hidden" />
<script>
   ????????????????
</script>

e

<input name="dataVencimentoTit" type="hidden" />
<script>
    ????????????????
</script>

Obs: it can't be PHP, because I'm using this code inside a code block of the theme, in WordPress. Inside there is no PHP code, only JavaScript.

Answer:

How to set a date in one input and another, fifteen days later in another?

The steps you need to follow are:

• create a date object with the start day
• create a new date object 1296e6 longer than the other (because JavaScript works in milliseconds)
• have a function to format the output string, in this case YYYYMMDD
• go to the DOM "fetch" the elements and set their .value

In practice:

function pad(s) {
    return (s < 10) ? '0' + s : s;
}

function formatarData(d) {
    return [d.getFullYear(), d.getMonth() - 1, d.getDate()].map(pad).join('');
}

var emissao = document.querySelector('input[name="dataEmissao"]');
var vencimento = document.querySelector('input[name="dataVencimentoTit"]');

var hoje = new Date();
var quinzeDias = new Date(hoje.getTime() + 1296e6);
emissao.value = formatarData(hoje);
vencimento.value = formatarData(quinzeDias);

Example: https://jsfiddle.net/3zymmpxb/1