extensions/amp-iframe/amp-iframe-vs-native-iframe.md
amp-iframe has been an AMP component since ~2015. It was designed to make native iframes more secure and impove user experience by enforcing restrictions on it's position outside the top 75% or 600px in an AMP document. With the migration of amp-iframe to Bento, we want to assess if we can retire amp-iframe component in favor of native iframes, which now support features like lazy loading. An option would be to support both, but for users it would be confusing which to use when, potentially impacting page experience of AMP documents.
Not yet. There are several features not supported by native iframes, like the ones discussed below.
Currently, amp-iframe supports dynamic resizing i.e. updating the iframe height and/or width at runtime. This requires dispatching a postMessage from the iframe to the parent window that includes a payload with type="embed-size" and desired height as the height property. The parent window then requests the AMP runtime to accomodate the resize request when possible to reduce layout shift. Native iframes lack a standardized way to resize dynamically, especially in a manner that reduces layout shift.
amp-iframe also supports requesting and receiving consent data from the parent window if a consent management platform (CMP) is present. This works by dispatching a send-consent-data postMessage and receiving a consent-data message from the parent, allowing amp-iframe to block components based on the user's consent. This is a specific use case and there are currently no proposed standards to add support in native iframes.
Lazy loading using loading="lazy" attribute is currently only supported in Chromium based browsers (https://caniuse.com/loading-lazy-attr). Without polyfills, we lose this feature for non Chromium browsers.
Additionally, if and when implemented, the thresholds to lazy load resources may differ among browsers. Chrome, for example, takes into account connection type, whether Lite mode (previously known as "Data Saver" it improves loading speed on slow network connections and is only avilable for Chrome on Android) is enabled, etc. The differences between browser implementations may lead to inconsistent behavior if we choose to support native iframes with lazy loading.