Quick sketch of JS prototypal inheritance

prototypal-inheritance-demo.js

// A basic prototypal inheritance chain (ignores constructor chaining)
// If you ask for property 'a' on an object created from function 'C', it will check if the object has a property 'a'.
// If not, it will check if C's prototype (an instance of B) has a property 'a'.
// If not, it will check if B's prototype (an instance of A) has a property 'a' (which it will).

function A() { }
A.prototype.a = 'A'

function B(a, b) { }
B.prototype = new A();
B.prototype.b = 'B'

function C() { }
C.prototype = new B();
C.prototype.c = 'C'

// Some instances to play with. Note that only the 'd' property is set on each object.
var a1 = new A();
a1.d = 'A1';

var b1 = new B();
b1.d = 'B1';

var c1 = new C();
c1.d = 'C1';

console.log("=====a1===========");
console.log("a1.a", a1.a);
console.log("a1.b", a1.b);
console.log("a1.c", a1.c);
console.log("a1.d", a1.d);

console.log("=====b1===========");
console.log("b1.a", b1.a);
console.log("b1.b", b1.b);
console.log("b1.c", b1.c);
console.log("b1.d", b1.d);

console.log("=====c1===========");
console.log("c1.a", c1.a);
console.log("c1.b", c1.b);
console.log("c1.c", c1.c);
console.log("c1.d", c1.d);

// Directly set the 'a' property on c1. This overrides the original (prototype) value from A.
console.log("=====c1 override==");
c1.a = 'C1 (overridden)';
console.log("c1.a", c1.a);
console.log("c1.b", c1.b);
console.log("c1.c", c1.c);
console.log("c1.d", c1.d);

console.log("=====a1===========");
console.log("a1.a", a1.a);
console.log("a1.b", a1.b);
console.log("a1.c", a1.c);
console.log("a1.d", a1.d);

// Unset the 'a' property on c1. This reverts back to the original (prototype) value from A.
console.log("=====c1 revert====");
delete c1.a;
console.log("c1.a", c1.a);
console.log("c1.b", c1.b);
console.log("c1.c", c1.c);
console.log("c1.d", c1.d);

// Show the state of all the objects (note that it only shows directly-declared properties, not inherited ones).

console.log("=====Objects======");
console.dir(a1);
console.dir(b1);
console.dir(c1);

console.log("====Prototypes====");
console.dir(A.prototype);
console.dir(B.prototype);
console.dir(C.prototype);

the-output.txt

=====a1===========
a1.a A
a1.b undefined
a1.c undefined
a1.d A1
=====b1===========
b1.a A
b1.b B
b1.c undefined
b1.d B1
=====c1===========
c1.a A
c1.b B
c1.c C
c1.d C1
=====c1 override==
c1.a C1 (overridden)
c1.b B
c1.c C
c1.d C1
=====a1===========
a1.a A
a1.b undefined
a1.c undefined
a1.d A1
=====c1 revert====
c1.a A
c1.b B
c1.c C
c1.d C1
=====Objects======
A { d: 'A1' }
A { d: 'B1' }
A { d: 'C1' }
====Prototypes====
A { a: 'A' }
A { b: 'B' }
A { c: 'C' }