[Webkit-unassigned] [Bug 217949] New: resize event is not fired unless the DOM is fully loaded

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=217949

            Bug ID: 217949
           Summary: resize event is not fired unless the DOM is fully
                    loaded
           Product: WebKit
           Version: Safari 14
          Hardware: iPhone / iPad
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Frames
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: muodov at gmail.com

It seems like Safari on iOS/iPadOS does not trigger resize events until all the page resources are loaded.

Steps to reproduce:
1. Open http://x.zok.pw/ios-iframe-resize/parent.html
2. Press the "open slowchild" button
3. Observe that there is no messages about resize events inside the iframe

Expected behaviour: there should be a resize event detected at step 3.

The test page contains the second button "open child", which opens a similar frame without slow resources. In this case, `onload` event is fired before the resize, and resize event is correctly fired inside the frame.

Notes:
I could reproduce this bug only on iOS. Desktop Safari, Chrome and Firefox trigger the resize vent as expected.

According to the HTML spec (Step 4 of https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering), user agent can decide to skip the resize steps, but in this case the viewport has actually changed. This is also detected in the test page.

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