[webkit-dev] Odd behavior with instrumentation of WebKit

Gregor Richards gkrichar at purdue.edu
Tue Mar 15 15:38:58 PDT 2011

On 03/15/2011 06:31 PM, Darin Adler wrote:
> On Mar 15, 2011, at 8:16 AM, Gregor Richards wrote:
>> We maintain an instrumented branch of WebKit to do various dynamic measurements of JavaScript. One of our changes which should have no semantic effect on the behavior of JS is actually causing a visible change in the behavior of (at least) http://about.com/ . The visible difference is that the menus don't work, and the underlying reason seems to be that Array.prototype.slice is (rather inexplicably) being rewritten to undefined, causing further code to fail. I've worked the issue down to a single line
> It’s good that you reduced your JavaScript changes down to a single line. Next step would be to make a local copy of the about.com site, reproduce the bug with that, and then reduce it as well. Once you do that it you can get to the bottom of it quickly.
>      -- Darin
I hadn't done that yet because at this point I wasn't sure whether it 
was our bug or not. I just wanted to know whether I was correct in my 
assumption that these changes should not induce a behavioral difference. 
If that's the case, then absolutely I'll try to create a minimal test case.

  - Gregor Richards

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