Embeds not working in IE 11

[Fencer04]

When using Twenty Seventeen oEmbeds from WordPress links don't show the box and style in Internet Explorer 11.

[Fencer04]

Chrome view vs. IE 11 view.

[swissspidy]

Hey there,

Thanks for your report! Would you mind sharing a screenshot of the visual inconsistencies?

Edit: Just saw the screenshot now :-)

[swissspidy]

The problem you're having is not about missing styles. Instead, the iframe is not being loaded at all.

WordPress embeds consist of two parts: a <blockquote> element and an <iframe>. The quote is shown by default and eventually replaced by the iframe if it loads successfully. To be more precise, the iframe sends a message to the embedding site when it's been loaded completely to say it's ready.

So on your second screenshot, the iframe is not loaded for some reason. I just tested embeds on IE 11 as well and it turns out the browser never reaches the line where the security attribute should be removed for IE 10 and IE 11. Why? WordPress always adds the data-secret attribute in wp_filter_oembed_result(), this the check in wp-embed.js is flawed.

Looks like this has been broken all the way since 4.4 :-( Perhaps introduced in [35577].

Pinging @pento.

[pento]

I'm a little surprised that this managed to be broken for so long, but I agree that [35577] is the likely culprit.

38694.diff​ looks good as a fix.

[swissspidy]

@pento Actually, it was [35708]. Memories.

[swissspidy]

In 39347:

Embeds: Correctly remove security attribute from iframes in IE 10 and IE 11.

This was originally added in 4.4, but presumably broke with [35708], which prevented these browsers from actually reaching the relevant code section.
Let's make embeds work again in IE 10 and IE 11.

Fixes #38694.