gistfile1.js

function A(name) {
  this.name = name;
}

A.prototype.b = function(lastName) {
  this.lastName = lastName;
  console.log(this.name + " " + this.lastName);
}

a1 = new A("Howard");
a2 = new A("Vance");

b1 = new a1.b("H");  // access to a parent object lost. this.name == undefined
b2 = new a2.b("I");