JSFiddle - React, Tailwind, and code Playground

HTML

<div id="datepicker">
    <div>
        <span class="day">3</span>
        <span class="day active">4</span>
        <span class="day">5</span>
    </div>

    <div>
        <span class="month">May</span>
        <span class="month active">Jun</span>
        <span class="month">Jul</span>
    </div>
        
    <div>
        <span class="year">2013</span>
        <span class="year active">2014</span>
        <span class="year">2015</span>
    </div>
</div>
<input type="text" name="fecha">

CSS

.active{
    color: red;
}

JavaScript

var spans = $("#datepicker div span"),
    total = spans.length,
    fecha = $("input[name=fecha]"),
    day, month, year;

for (i = 0; i < total; i++) {
    if (spans[i].className == "day active")
        day = spans[i].innerHTML + "/";
    if (spans[i].className == "month active")
        month = spans[i].innerHTML + "/";
    if (spans[i].className == "year active")
        year = spans[i].innerHTML;
}

fecha.val(day + month + year);