What datastructure i Javascript will work like this? :

ROLES.ADMIN return "admin" ROLES.ADMIN.TESTERS returns "admin.testers"

I tried with an object but the was no good.

ROLES = {
  ADMIN:{
    TESTERS:"testers",
    BOSS:"boss"
  }
}

As you can see..i need some sort of datastructure that also gives me a value for the key ADMIN, as well as the ADMINS sub values.