Same Origin Policy & iframe

Mariko Kosaka

In this codelab, see how the same-origin policy works when accessing data inside an iframe.

Set up: Page with a same-origin iframe

This page embeds an iframe, called iframe.html, in the same origin. Since the host and the iframe share the same origin, the host site is able to access data inside of the iframe and expose the secret message like blow.

const iframe = document.getElementById('iframe');
const message = iframe.contentDocument.getElementById('message').innerText;

Change to cross-origin iframe

Try changing the src of the iframe to Can the host page still access the secret message?

Since the host and embedded iframe do not have the same origin, access to the data is restricted.