[Webkit-unassigned] [Bug 69464] New: Browser update slowed down massively by specific (constant-speed) jQuery code

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Wed Oct 5 14:24:07 PDT 2011


           Summary: Browser update slowed down massively by specific
                    (constant-speed) jQuery code
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
               URL: http://phrogz.net/tmp/webkit-jquery-browser-update-slo
        OS/Version: Unspecified
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: New Bugs
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: gavin at phrogz.net

Created an attachment (id=109863)
 --> (https://bugs.webkit.org/attachment.cgi?id=109863&action=review)
Test case showing the problem.

Visit http://phrogz.net/tmp/webkit-jquery-browser-update-slowdown.html and follow the instructions there to test the slowdown.

Specifically, there are two distinct sets of jQuery objects, once with 100 <p> ("classes") and the other with 1500 <p> ("methods"). 

Calling methods.hide() followed by classes.filter(":visible") results in the web browser taking 40-400x longer to render the updates versus reversing the order of those statements. In both cases the amount of time seen in the JavaScript function is identical, as is the resulting effect on the DOM.

This slowdown is seen on both Safari and Chrome. It is not present on Firefox v7.
This was reproduced on Windows 7; it is unknown if this affects other OS or not.
This slowdown is not present when using a different jQuery filter with the same effect (e.g. classes.filter(".shown")). It is specific to the jQuery/Sizzle code surrounding the :visible pseudo-class selector.

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