Guard against Webkit's extraneous calls to xhr.onreadystatechange #633
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I would be more motivated to accept a workaround for am obscure WebKit issue if it was filed in their issue tracker. |
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I've filed a bug with Chorme based on the info I have: http://code.google.com/p/chromium/issues/detail?id=159827 It references the Webkit reports I've found around the web. Good luck with your project. |
mislav
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Nov 13, 2012
The bug is present in Chrome 23.0.1271.64 and possibly iOS 6, and is reproducible using the debugger but otherwise occurs randomly. References #633 http://code.google.com/p/chromium/issues/detail?id=159827
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OK, I think I just seen the issue in the wild while using GitHub.com: an ajax callback got executed twice in jQuery. Pulled your fix. Thanks! |
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Great! Thanks a lot Mislav! |
lopper
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Apr 24, 2013
The bug is present in Chrome 23.0.1271.64 and possibly iOS 6, and is reproducible using the debugger but otherwise occurs randomly. References madrobby#633 http://code.google.com/p/chromium/issues/detail?id=159827
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In certain cases Webkit will call the onreadystatechange method of a single XMLHttpRequest object multiple times indicating that it is ready (readyState == 4).
This results in Zepto's 'success' or 'error' methods being called multiple times for the same AJAX request.
This is documented in this thread:
http://stackoverflow.com/questions/12761255/can-xhr-trigger-onreadystatechange-multiple-times-with-readystate-done
with a jsfiddle here:
http://jsfiddle.net/44b3P/
and confirmed here:
http://osdir.com/ml/general/2012-10/msg12396.html
To reproduce in Zepto:
Expected: you should see 1 alert with the text 'error'
Actual: the alert with the text 'error' occurs 3 times
I'm working to find a way to reproduce this and submit upstream (at least to Chrome -- maybe to Webkit? -- We think it's a Webkit bug since we first observed this issue in Safari on iOS 6).
In the meantime this patch should resolve the issue in Zepto.
[1] While this is an awkward way to reproduce (clearly a debugger statement shouldn't be in production code) we've observed similar behavior in our production code where success functions are called multiple times for the same AJAX request -- usually when there's a lot going on on the page or the page hasn't completed loading.
The 'debugger' statement was the most reliable way I've seen to approximate these conditions and reproduce the behavior.