function resizeIframe(obj){
    obj.contentWindow.postMessage({action: 'getDocumentHeight', targetElementId: obj.id}, '*');
}

window.addEventListener('message', function (event) {
    document.getElementById(event.data.targetElementId).style.height = (event.data.documentHeight + 35) + 'px';
});

document.addEventListener("DOMContentLoaded", function(event) {
    var ifrm = document.createElement('iframe');
    ifrm.setAttribute('id', 'widget-iframe-8794');
    ifrm.setAttribute('width', '100%');
    ifrm.setAttribute('height', '0');
    ifrm.setAttribute('scrolling', 'no');
    ifrm.frameBorder=0;
    ifrm.setAttribute('onload', 'resizeIframe(this)');

    var el = document.getElementById('3');
    el.appendChild(ifrm);
    ifrm.setAttribute('src', 'https://rankingi.rp.pl/widget/builder?token=6733d1daa049f447c33c208653938a98cc78006b29dd31f5456b2');
});