JSFiddle - React, Tailwind, and code Playground

HTML

<a id="iframe">test</a><br>
<iframe id="iframe">test</iframe>

JavaScript

var d=new Date();
var day=d.getDate() -13;
var month=d.getMonth() +1;
var year=d.getFullYear();
var vse = (year +"0"+  month + "" + day);

document.getElementById('iframe').href= 'http://orthochristian.com/calendar/'+vse+'.html';
document.getElementById('iframe').src= 'http://orthochristian.com/calendar/'+vse+'.html';