JSFiddle - React, Tailwind, and code Playground

by gilly3

HTML

<input>
<div><span>unknown</span> days old</div>

JavaScript

function validateDOB(element) {
    var valid = false;

    var today = new Date();
    var dd = today.getDate();
    var mm = today.getMonth() + 1; //do that January is NOT represented by 0! 
    var yyyy = today.getFullYear();

    if (dd < 10) {
        dd = '0' + dd;
    }
    if (mm < 10) {
        mm = '0' + mm;
    }

    $("span").text("unknown");

    var today = mm + '/' + dd + '/' + yyyy;
    if (element.value != today) {
        var days = 0;
        var difference = 0;

        today = new Date();

        difference = today - new Date(element.value);

        days = Math.round(difference / (1000 * 60 * 60 * 24) - 1);
        $("span").text(days);
        valid = true;
    }
}
$(function(){
    $("input").change(function(){
        validateDOB(this);
    });
});