The following code behaves incorrectly (inconsistent with the standard and other engines) in Chakra due to a missing cache update:

 function Base() { } Base.prototype = { f() { return "Base " + this.toString(); }, x: 15, toString() { return "this is Base"; } }; function Derived() { this.derivedDataProperty = "xxx"; } Derived.prototype = { __proto__: Base.prototype, toString() { return "this is Derived"; }, x: 27, f() { var a = super.x; print(this.x); return "Derived"; } }; print(new Base().f()); print(new Derived().f()); 

It should print 27 as the value of Derived.x, but instead prints 15. This code hits an assert in the debug build:

ASSERTION 5639: (/home/user/test_everywhere/ChakraCore/lib/Runtime/Types/TypePropertyCache.cpp, line 277) *propertyValue == JavascriptOperators::GetProperty(propertyObject, propertyId, requestContext)
Failure: (*propertyValue == JavascriptOperators::GetProperty(propertyObject, propertyId, requestContext))
Illegal instruction (core dumped)