JSFiddle - React, Tailwind, and code Playground

HTML

<span class="job-date">1-14-2013</span>

<div class="message">This job is <span class='day-difference'></span> days old it may no longer be available</div>

JavaScript

var jobDate  =  new Date($('.job-date').text());
var today = new Date();
var dayDifference = ((today - jobDate) / (1000 * 60 * 60 * 24));
if (dayDifference >= 30) {
    $('.message').show().find('.day-difference').text(dayDifference.toFixed(0));
}
else {
    $('.message').hide();
}