I need to merge my html within another html page (another website) in a form of an iframe.

I need get the id of the iframe tag in the website inside my index.html.

I am not sure if this is achievable, but here is what I was trying to do

window.parent.document.getElementsByTagName('iframe')[0].getAttribute('id')

but I go this error:

Blocked a frame with origin "https://website.com" from accessing a cross-origin frame. 

here is an image that shows the iframe tag on the website. src in the iframe tag is changed just for not showing the website domain.