How do I test an iframe and get all the response headers?

I am working on a webapp that can show url's in an iframe. But it also has the ability to first test the url before showing the url in an iframe. So before i show the iframe (set CSS rule to show the iframe element) i want to wait on the response. If i get an error or if i get a response header 'x-frame-options: DENY' i don't want to show the iframe and instead show an error message or something.

Consider this example:

const request = new XMLHttpRequest();
request.open("GET", urlToTest, true);
request.send();

Here i ALWAYS get a CORS issues. But this is expected, and testing this is not the same as what we actually want to do which is:

<iframe id="webiframe" "src"="urlToTest></iframe>

Then i tried the following:

this.webiframe is a reference of the <iframe>

this.webiframe.onload = function () {
    console.log('iframe ONLOAD');
}.bind(this);
this.webiframe.onerror = function () {
    console.log('iframe ONERROR');
}.bind(this);
this.webiframe.contentDocument.onreadystatechange = function () {
    this.iFrameEvent();
}.bind(this);
this.webiframe.contentDocument.addEventListener('DOMContentLoaded', this.iFrameEvent);
this.webiframe.contentDocument.addEventListener('load', this.iFrameEvent);
this.webiframe.contentDocument.addEventListener('onreadystatechange ', this.iFrameEvent);

But the event listeners that are added to the contentDocument are never called. The only event that is called is the onload event of the iframe reference.

So my question:

Is it possible to get some information/testing of iframe when setting a 'src' attribute on it. More specifically if the url is working and if not, why it's not working through response headers?