zoo.js

function Animal(type, limbs){
  this.type = type;
  this.limbs = limbs;
}

Animal.prototype.identify = function {
  console.log("I am a " + this.type + "with " + this.limbs +" legs.");
};

function Zoo(){
  
};

Zoo.prototype.init(){
  this.animals = animals;
};

Zoo.prototype.bipeds = function(){
  var bipeds = [];
  for(var i = 0, i < animals.length; ++i){
    if(animals[i].limbs == 2)
      bipeds.push(animals[i]);
  }
  return bipeds
};

Zoo.prototype.quadrupeds = function(){
  var quadrupeds = [];
  for(var i = 0, i < animals.length; ++i){
    if(animals[i].limbs ==4)
      quadrupeds.push(animals[i]);
  }
  return quadrupeds
};


function assert(test, message) {  
  if (!test) {
    throw "ERROR: " + message;
  }
  return true;
}
 
var animals = [
  new Animal("Human", 2),
  new Animal("Monkey", 2),
  new Animal("Kangaroo", 2),
  new Animal("Horse", 4),
  new Animal("Cow", 4),
  new Animal("Centipede", 100)
];
 
Zoo.init(animals);
 
assert(
  Zoo.bipeds().length === 3, "the Zoo should have 3 bipeds"
);
assert(
  Zoo.quadrupeds().length === 2, "the Zoo should have 2 bipeds"
);
assert(
  animals[0].identify() === "I am a Human with 2 legs.", "humans have 2 legs"
);
assert(
  animals[2].name === "Kangaroo", "expected 'Kangaroo'"
);
assert(
  animals[0].identify === animals[5].identify, "only one implementation of the identify() function should exist"
);