188083 2018-07-26 15:47:17 -0700 The instanceof operator does not work as expected for classes that extend CustomEvent or Event 2020-03-22 10:25:17 -0700 1 1 1 Unclassified WebKit JavaScriptCore Safari Technology Preview Mac Unspecified RESOLVED CONFIGURATION CHANGED https://bugs.webkit.org/show_bug.cgi?id=174313 InRadar P2 Normal --- 1 ekashida webkit-unassigned ashvayka cdumez keith_miller rniwa webkit-bug-importer oldest_to_newest 1445577 0 ekashida 2018-07-26 15:47:17 -0700 Overview: class FooEvent extends CustomEvent { constructor() { super('foo'); } }; var foo = new FooEvent(); console.log('This evaluates to "false" which is unexpected', foo instanceof FooEvent); console.log('This evaluates to "true" which is expected', foo instanceof CustomEvent); console.log('This evaluates to "true" which is expected', foo instanceof Event); Expected Results: The instanceof operator, when given an instance of FooEvent which extends CustomEvent, and the FooEvent constructor, should evaluate to "true". Build Date & Hardware: Release 61 (Safari 12.0, WebKit 13606.1.25.1) Mac OS 10.13.6 1446783 1 rniwa 2018-07-31 19:06:50 -0700 I don't think class inheritance ever worked with Event's. 1447021 2 ekashida 2018-08-01 15:12:28 -0700 It seems to be working as expected in Firefox and Chrome, and Edge has the following open issue: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/11923584/ 1632653 3 ashvayka 2020-03-22 10:24:58 -0700 (In reply to Eugene Kashida from comment #0) > Expected Results: > > The instanceof operator, when given an instance of FooEvent which extends > CustomEvent, and the FooEvent constructor, should evaluate to "true". As of https://trac.webkit.org/changeset/256716, extending CustomEvent (as well as other DOM constructors) works as expected. 1632656 4 webkit-bug-importer 2020-03-22 10:25:17 -0700 <rdar://problem/60743143>