gistfile1.txt

Given object X
Given type A

if X isa A, BUT X.m isnot A::m
then I am unhappy.

For example (classical):

class A { func one() { return 1 } }
class B : A { func one() { return 2 } }

X = new B()

X isa A (true)
X.one !== A::one (true)
--> I'm unhappy.

For example (prototypal):

class A { func one() { return 1 } }
X.prototype = A;
X.one = func() { return 2 }

X isa A (true since X.prototype === A)
x.one !== A.one (true)
--> I'm unhappy