prototype_inh.js

gistfile1.js

var shape = {
  type: "",
  getType: function () {
    return this.type;
  },
};

function Triangle(a, b, c) {
  this.type = "triangle";
  this.a = a;
  this.b = b;
  this.c = c;
}

Triangle.prototype = shape;

Triangle.prototype.constructor = Triangle;

Triangle.prototype.getPerimeter = function () {
  return this.a + this.b + this.c;
};

var t = new Triangle(1, 2, 3);

console.log(shape.isPrototypeOf(t));
console.log(t.getPerimeter());
console.log(t.getType());
console.dir(t.constructor);