contract Adoption {
    address[16] public adopters;

    function adopt(uint petId) public returns (uint) {
        require(petId >= 0 && petId <= 15);
        adopters[petId] = msg.sender;
        return petId;
    }

    function getAdopters() public returns (address[16]) {
        return adopters;
    }
}

App.contracts.Adoption.deployed().then(function(instance) {
    adoptionInstance = instance;
    return adoptionInstance.adopt(petId, {from: account});
  })