Implement a Queue

Implement a queue with enqueue, dequeue, front, and isEmpty methods. enqueue(val) adds to back, dequeue() removes and returns front (null if empty), front() returns front without removing (null if empty), isEmpty() returns boolean.

q = createQueue(); q.enqueue(1); q.enqueue(2); q.front() => 1; q.dequeue() => 1; q.dequeue() => 2