Get element from within an iFrame

var iframe = document.getElementById('iframeId');
var innerDoc = (iframe.contentDocument) ? iframe.contentDocument : iframe.contentWindow.document;

You could more simply write:

var iframe = document.getElementById('iframeId');
var innerDoc = iframe.contentDocument || iframe.contentWindow.document;

and the first valid inner doc will be returned.

Once you get the inner doc, you can just access its internals the same way as you would access any element on your current page. (innerDoc.getElementById...etc.)

IMPORTANT: Make sure that the iframe is on the same domain, otherwise you can't get access to its internals. That would be cross-site scripting.

If iframe is not in the same domain such that you cannot get access to its internals from the parent but you can modify the source code of the iframe then you can modify the page displayed by the iframe to send messages to the parent window, which allows you to share information between the pages. Some sources:

• https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage
• Html5 - Cross Browser Iframe postmessage - child to parent?
• cross site iframe postMessage from child to parent

You can use this function to query for any element on the page, regardless of if it is nested inside of an iframe (or many iframes):

function querySelectorAllInIframes(selector) {
  let elements = [];

  const recurse = (contentWindow = window) => {

    const iframes = contentWindow.document.body.querySelectorAll('iframe');
    iframes.forEach(iframe => recurse(iframe.contentWindow));
    
    elements = elements.concat(contentWindow.document.body.querySelectorAll(selector));
  }

  recurse();

  return elements;
};

querySelectorAllInIframes('#elementToBeFound');

Note: Keep in mind that each of the iframes on the page will need to be of the same-origin, or this function will throw an error.

Below code will help you to find out iframe data.

let iframe = document.getElementById('frameId');
let innerDoc = iframe.contentDocument || iframe.contentWindow.document;