137407 2014-10-03 14:50:34 -0700 window.performance object resets script-applied properties 2016-09-12 14:25:23 -0700 1 1 1 Unclassified WebKit WebCore JavaScript 528+ (Nightly build) Mac (Intel) Other RESOLVED FIXED http://jsfiddle.net/dss8wudw/3/ P2 Normal --- 1 eanakashima cdumez achristensen alex.christensen ap aroben cdumez commit-queue darin esprehn+autocc ggaren godfreykfc hartman.wiki kondapallykalyan krinklemail rniwa sam oldest_to_newest 1039361 0 eanakashima 2014-10-03 14:50:34 -0700 To polyfill certain browser APIs that are not fully implemented in WebKit, including the User Timing API, it's useful to be able to add properties to the `window.performance` object, using code like `window.performance.mark = function() { [implementation here] }`. In Safari 8 we're seeing a behavior where the `window.performance` object is periodically reset, removing all properties applied with scripts. The point when the reset occurs can vary, but it seems to correlate to: - opening and closing the developer tools (console) - a change in the document readyState - triggering certain DOM events, e.g. clicking back on the document after you've opened the developer tools Admittedly it's questionable whether to consider this a bug, since it's typically considered a best practice to not modify built-in browser-provided objects. But it would be really helpful to be able to do this reliably in the case of polyfills. Steps to Reproduce: 1. Set a property of `window.performance` in a script or in the console. For example, `window.performance.example = "example"` 2. `console.log(window.performance.example)` and see "example" printed 3. Open and close the developer tools (console) a few times. 4. `console.log(window.performance.example)` and see "undefined" printed See this JS Fiddle http://jsfiddle.net/dss8wudw/3/ for demo setup. Expected Results: Ideally `window.performance` properties would remain set unless they are modified by a script (or the user refreshes or navigates to a new page). The value of `window.performance.example` should remain `"example"` until we delete it or set it to something else. Configuration: Browser: Safari Version 8.0 (10600.1.22) OS: Mac OS X 10.10 Device: MacBook Air (11-inch, Mid 2012) 1039513 1 alex.christensen 2014-10-04 11:26:53 -0700 I think this is an issue with the JavaScript bindings and not with the underlying C++ object that is wrapped, and it may be intentionally resetting something. Are there other built-in browser-provided objects that have similar behavior? I unfortunately don't have access to build WebKit on Yosemite right now, but I could look into something that behaves similarly on Mavericks. 1039519 2 ap 2014-10-04 11:54:14 -0700 Bug 122770 could be an example, it fixed the same problem for window.crypto. 1125752 3 krinklemail 2015-09-14 15:08:39 -0700 Downstream report from Wikimedia where this caused fatal exceptions for Safari users reading Wikipedia: https://phabricator.wikimedia.org/T112287#1638614 Test case: http://codepen.io/Krinkle/debug/YywQJb It has three checkpoints: 1) Immediately after definition. 2) From a <script src> loaded script. 3) After window.onload. In Safari 8.0.8, sometimes 'performance.mark' is defined at all thee, sometimes only at #1, sometimes at #1 and #2. 1125756 4 hartman.wiki 2015-09-14 15:15:42 -0700 Also confirmed as a problem in Version 9.0 (10601.1.56) btw. 1228800 5 godfreykfc 2016-09-12 11:00:31 -0700 There is still an issue in 9.1.3 1228850 6 cdumez 2016-09-12 12:22:29 -0700 I'll take a look soon. 1228864 7 288603 cdumez 2016-09-12 13:09:04 -0700 Created attachment 288603 Patch 1228879 8 darin 2016-09-12 13:54:39 -0700 We can recommend a workaround for affected sites if they want to work properly with older versions of WebKit. I think that putting this line of code in will work around the bug: window.keepPerformanceAlive = window.performance; 1228880 9 darin 2016-09-12 13:55:20 -0700 Note, that’s just a guess. Someone would need to test to be sure that works! 1228896 10 288603 commit-queue 2016-09-12 14:25:17 -0700 Comment on attachment 288603 Patch Clearing flags on attachment: 288603 Committed r205823: <http://trac.webkit.org/changeset/205823> 1228897 11 commit-queue 2016-09-12 14:25:23 -0700 All reviewed patches have been landed. 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