Answers for "use javascript inside iframe"

how to get element in iframe using javascript

const iframe = document.getElementById("myIframe");

const iWindow = iframe.contentWindow;
const iDocument = iWindow.document;

// accessing the element
const element = iDocument.getElementsByTagName("p")[0];
element.style.color = "green";

run javascript in iframe

let script=document.createElement('script');
script.innerText=`your script`
document.querySelector('iframe').appendChild(script)