Shallow Inheritance in JavaScript

shallowInheritance.js

var A = function (neighborhood) {
  this.neighborhood = neighborhood;
}
A.prototype.getInitial = function () {
  return this.neighborhood[0];
}
A.prototype.getLast = function () {
  return this.neighborhood[this.neighborhood.length-1];
}

var B = function (neighborhood) {
  A.call(this, neighborhood.concat('!'));
}
B.prototype = A.prototype;
B.prototype.getExclamatoryInitial = function () {
  return this.getInitial().concat(this.getLast());
}

var a = new A('Shinagawa');
var b = new B('Shinagawa');

try {
    console.log(a.getExclamatoryInitial());
  } catch(e) {
    e && console.log(e);
  }

  console.log(b.getExclamatoryInitial());

delete A.prototype.getExclamatoryInitial;



B.prototype = Object.create(A.prototype);
B.prototype.getExclamatoryInitial = function () {
  return this.getInitial().concat(this.getLast());
}

var a = new A('Shinagawa');
var b = new B('Shinagawa');

try {
    console.log(a.getExclamatoryInitial());
  } catch(e) {
    e && console.log(e);
  }

  console.log(b.getExclamatoryInitial());

/*
  Sa
  S!
  [TypeError: Object [object Object] has no method 'getExclamatoryInitial']
  S!
*/