Javascript Object Inheritance Extend Utility Method

function Animal() {}

Animal.prototype = {// w ww . ja  v  a2s  . c om
    group: "",
    gender: "",
    eat: function() {
        return "eat";
    },
    sleep: function() {
        return "zzzzzzzz..";
    }
}

function Bird(gender) {
  this.gender = gender;
}

function extend(subClass, superClass)
{
    // Create a new class that has an empty constructor
    // with the members of the superClass
    function inheritance() {};
    inheritance.prototype = superClass.prototype;
    // set prototype to new instance of superClass
    // _without_ the constructor
    subClass.prototype = new inheritance();
    subClass.prototype.constructor = subClass;
    subClass.baseConstructor = superClass;
    // enable multiple inheritance
    if (superClass.__super__) {
        superClass.prototype.__super__ = superClass.__super__;
    }
    subClass.__super__ = superClass.prototype;
}
extend(Bird, Animal);

Bird.prototype.eat = function() {
  // since birds like to "caw!" after eating we need to mask this function
  return Bird.__super__.eat.apply(this) + "... caw!";
}

let flamingo = new Bird("male");

console.log(flamingo.eat());