Hi, I checked this test which is now present in location (Webkit\LayoutTests\canvas\philip\tests\type.prototype.html) and online location http://philip.html5.org/tests/canvas/suite/tests/type.prototype.html with webkit revision on Windows 7 Last Changed Rev: 95852 Last Changed Date: 2011-09-23 15:56:21 -0400 (Fri, 23 Sep 2011) This test fails on Safari 5.1 and Firefox but passes on Opera. The test fails because webkit does not allow the deletion of property "getContext" via script delete window.HTMLCanvasElement.prototype.getContext; The reason is - "getContext" has attribute "DontDelete | Function" so it does not permit the script to delete this property. But I could not find any reference in WHATWG website whether this deletion should be allowed ??

As mentioned in http://www.w3.org/TR/2011/WD-WebIDL-20110927/#interface-prototype-object "There must exist an interface prototype object for every interface defined, regardless of whether the interface was declared with the [NoInterfaceObject] extended attribute. The interface prototype object for a particular interface has properties that correspond to the attributes and operations defined on that interface 4.5.6. Operations For each unique identifier of an operation defined on the interface, there must be a corresponding property on the interface prototype object (if it is a regular operation) or the interface object (if it is a static operation), The property has attributes { [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: true }. " In our case interface : JSHTMLCanvasElement

As mentioned in the latest W3C Web IDL specification http://www.w3.org/TR/2011/WD-WebIDL-20110927/#interface-prototype-object "There must exist an interface prototype object for every interface defined, regardless of whether the interface was declared with the [NoInterfaceObject] extended attribute. The interface prototype object for a particular interface has properties that correspond to the attributes and operations defined on that interface 4.5.6. Operations For each unique identifier of an operation defined on the interface, there must be a corresponding property on the interface prototype object (if it is a regular operation) or the interface object (if it is a static operation). The property has attributes { [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: true }." So in our case the interface : JSHTMLCanvasElement interface prototype : JSHTMLCanvasElementPrototype operation : getContext Correct me if I am wrong, shouldn't getContext be [[Configurable]]: true and hence we should be able to delete the property ??

please ignore this comment - typo

This appears to be working now with Safari Technology Preview 14 on macOS Sierra.