Bug 270736 – 3rd level iframe does not fire load event

• Component: DOM
• Status: RESOLVED DUPLICATE

3rd level iframe behaves differently than others.

Load events of iframe1 and iframe2 fire normally, iframe3 load event does not.

Steps to reproduce:
1. Open `about:blank`
2. Run following code
      (async () => {
        const iframe1 = document.createElement("iframe");
        iframe1.setAttribute("srcdoc", "");
        document.body.append(iframe1);
        await new Promise((resolve) =>
          iframe1.addEventListener("load", resolve, { once: true })
        );

        const iframe2 = document.createElement("iframe");
        iframe2.setAttribute("srcdoc", "");
        iframe1.contentDocument.body.append(iframe2);
        await new Promise((resolve) =>
          iframe2.addEventListener("load", resolve, { once: true })
        );

        const iframe3 = document.createElement("iframe");
        iframe3.setAttribute("srcdoc", "");
        iframe2.contentDocument.body.append(iframe3);
        await new Promise((resolve) =>
          iframe3.addEventListener("load", resolve, { once: true })
        );
        console.log("loaded");
      })();

Created attachment 470283 [details]
10 iframe levels - srcdoc

This document shows how WebKit renders just 2 levels, while other browsers render all the levels.

[Radar WebKit Bug Importer]

<rdar://problem/124757843>

[Ahmad Saleem]

Test on 305423@main and it seems to work now. Fixed with 305421@main (confirmed with reverting and we fail without fix).

*** This bug has been marked as a duplicate of bug 305276 ***