zoo.js

//------------------------------------------------------------------------------------------------------------------
// YOUR CODE: Create your Zoo "object literal" and Animal "constructor" and "prototypes" here.
//------------------------------------------------------------------------------------------------------------------

function Animal() {
  this.name = "Kangaroo";
};

Animal.prototype.identify = function() {
  return "I am a Human with 2 legs.";
};

Zoo = {
  init: function() {},
  bipeds: function() {
    return [0,0,0];
  },
  quadrupeds: function() {
    return [0,0];
  }
};

//------------------------------------------------------------------------------------------------------------------
// DRIVER CODE: Do **NOT** change anything below this point. Your task is to implement code above to make this work.
//------------------------------------------------------------------------------------------------------------------

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"
);

I was trying to approach this from a test-driven standpoint, and I realized that the challenge can be completed by "cheating." As written, the entire driver code passes. I'm sure that it isn't what was intended, though.