Server names consist of an alphabetic host type (e.g. "apibox") concatenated with the server number, with server numbers allocated as before (so "apibox1", "apibox2", etc. are valid hostnames).
Write a name tracking class with two operations, allocate(host_type) and deallocate(hostname). The former should reserve and return the next available hostname, while the latter should release that hostname back into the pool.
For example:
>> tracker = Tracker.new
>> tracker.allocate('apibox')
"apibox1"
>> tracker.allocate('apibox')
"apibox2"
>> tracker.deallocate('apibox1')
nil
>> tracker.allocate('apibox')
"apibox1"
>> tracker.allocate('sitebox')
"sitebox1"
How do I implement this is JavaScript?