JSFiddle - React, Tailwind, and code Playground

HTML

<iframe id='pag' src="" width="800px" height="400px" ></iframe>
<a href="#" onclick="cargar_pagina()">Cargar</a>

JavaScript

function cargar_pagina(){
    
   var ifr = document.getElementById('pag');
    ifr.src = 'http://www.forosdelweb.com/f13/funcion-para-cargar-contenido-iframe-988557/';
    }