zoo.js

function assert(test, message) {  
  if (!test) {
    throw "ERROR: " + message;
  }
  return true;
}

function Animal(name, legs){  
  this.name = name;  
  this.legs = legs;  
}  

Animal.prototype.identify = function() {
  return("I am a "+ this.name + " with " +this.legs+ " legs.");

};
var Zoo = {
  init: function(animals){
    this.animals = animals;
  }
}

Zoo.bipeds = function() {
  bipeds = [] 
  for (i = 0; i < this.animals.length; i++) {
    if (this.animals[i].legs === 2) {
      bipeds.push(this.animals[i]);
    }
   }
  return bipeds
};



Zoo.quadrupeds = function() {
  quadrupeds = [];
  for (i = 0; i < this.animals.length; i++){
    if (this.animals[i].legs === 4){
     quadrupeds.push(this.animals[i]);
   }
 }
 return quadrupeds
};


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"
  );