Bug 156585 – img onload event is fired upon receiving a 301

• Component: Page Loading
• Status: NEW

[Myles C. Maxfield]

1. Use the Network Link Conditioner (http://nshipster.com/network-link-conditioner/) to make the network slow
2. Open the reproduction html
3. Click somewhere
4. Wait a little while

Actual behavior: Red rectangle gets very narrow for a split second before jumping back to its original size

Expected behavior: Red rectangle never changes size

Firefox / Chrome display the expected behavior.

The link that we load when clicking (https://placehold.it/200x200) returns a 301. Initial guess is that we're firing the onload event upon receiving the 301, rather than the subsequent 200.

[Myles C. Maxfield]

This was reported by https://twitter.com/jordan_thomas/status/720270360944357377

[Myles C. Maxfield]

Created attachment 276408 [details]
Reproduction

[Radar WebKit Bug Importer]

<rdar://problem/25731182>

[Radar WebKit Bug Importer]

<rdar://problem/25731147>

[Brady Eidson]

This must be a regression. Would be great if somebody could pinpoint when.

[Alex Christensen]

If this is a regression, it's been in a while.  On Chrome I see no flash, on Firefox I see a blue flash, and on Safari I see a flash of the rectangle of a different size.  Also, from similar tests I'm pretty sure the 301 is not initiating the onload, but from reading the JavaScript it seems like that's what's going on.

I opened the reproduction html in v6.0.5 (7536.30.1) and see the "bounce" behavior there too. I also tried v5.1.9 (6534.59.8) and did _not_ see the behavior (although it does render the demo a little funky).