180006 2017-11-24 07:57:21 -0800 not a function, is 4.538223e-316 instead: function is optimized to a... number? 2017-11-27 14:58:10 -0800 1 1 1 Unclassified WebKit JavaScriptCore Safari 10 iPhone / iPad iOS 10.3 NEW P2 Normal --- 1 awerlang17 webkit-unassigned ap fpizlo saam oldest_to_newest 1374603 0 awerlang17 2017-11-24 07:57:21 -0800 # Overview: We're getting an exception where a function is expected but it's a number instead. The function is a class method part of Angular@4.3.6. Written in TypeScript and compiled to ES5 as (shortened to relevant bits): "use strict"; var Router = /** @class */ (function () { function Router() { } Router.prototype.serializeUrl = function (url) { return this.urlSerializer.serialize(url); }; return Router; }()); Couldn't it be a user-level code changing the function to become a number? I think not. I added the following code to initialization: // FIXME: attempt to troubleshoot this.router.serializeUrl is not a function on Safari const serializeUrl = router.serializeUrl; Object.defineProperty(router, 'serializeUrl', { configurable: false, get: () => serializeUrl, set: (value) => { throw new Error('this.router.serializeUrl = ' + value) }, }); Object.defineProperty(Router.prototype, 'serializeUrl', { configurable: false, get: () => serializeUrl, set: (value) => { throw new Error('Router.prototype.serializeUrl = ' + value) }, }); It failed again and this trap didn't run. How the function could be replaced without going through these paths? Because it happens after a few successful invocations of ditto function, I believe the culprit lies in the optimizer (of course, it's not a valid replacement for a function, so that makes me wonder why it happens) # Steps to Reproduce: Unfortunately, it's unpredictable when it's going to happen. The function in question runs a few times until the error occurs. It may not happen at all for a given user, but keeps happening. When it fails, it fails for the same function / call site every time. # Actual Results: An exception is thrown: TypeError: this.router.serializeUrl is not a function. (In 'this.router.serializeUrl(this.urlTree)', 'this.router.serializeUrl' is 4.538223e-316) The floating point number reported is different every time. # Expected Results: Function should be invoked w/o problems. # Build Date & Hardware: Sample user agent: Mozilla/5.0 (iPhone; CPU iPhone OS 10_3_3 like Mac OS X) AppleWebKit/603.3.8 (KHTML, like Gecko) Version/10.0 Mobile/14G60 Safari/602.1 # Additional Builds and Platforms: Wasn't reported on iOS Safari !== 10.x so far. Nor other browsers & platforms (okay on Mac OS X, Windows, Chrome, Firefox, Edge) # Additional Information: Reported as well at https://github.com/angular/angular/issues/16717. The Angular team dismissed the issue because policies. 1374621 1 ap 2017-11-24 11:22:17 -0800 Could you please provide a reproducible case? I don’t think that this kind of an issue can be fixed based on a description alone. 1374740 2 awerlang17 2017-11-26 09:52:13 -0800 I published at https://awerlang.github.io/webkit180006/ I'm afraid is not easy to reproduce it though, as it just happens. 1375144 3 ap 2017-11-27 14:58:10 -0800 Thank you! What specifically should I try on this webpage to see the problem? It's OK if it takes a reasonable number of tries to reproduce, but hopefully we won't need to be manually interacting with the page for hours until this happens.