Code Fellows XOR

xor.js

// Implement an exclusive OR function called `preferredName` that has the following interface:

var FirstName,
    LastName;

preferredName(FirstName, LastName);
// -> false

FirstName = 'Hank';

preferredName(FirstName, LastName);
// -> 'Hank'

LastName = 'Yates';

preferredName(FirstName, LastName);
// -> false

FirstName = '';

preferredName(FirstName, LastName);
// -> 'Yates'