Lua Notification Center (cocos2dx)

notification.lua

--[[
Why this package?
Cocos2d-x CCNotificationCenter is limited to one lua function callback (observer) per target (CCObject).
This simple Lua script wraps CCNotificationCenter and allows code like:
addObserver(foo,'eventname')
addObserver(foo2,'eventname')
]]--

-- The NotificationCenter (nc) table
local nc = {
    observers = {},
    center = CCNotificationCenter:sharedNotificationCenter(),
    obj = CCNode:create() -- Can't use a CCObject because no constructor available in lua (e.g. CCObject:new or CCObject:create())
}
nc.__index = nc

function nc:post(event)
    -- Post a nil event will crash
    if event then
        self.center:postNotification(event)
    end
end

function nc:observerExists(func,event)
    for k,v in ipairs(self.observers[event]) do
        if func == v then
            return k
        end
    end
    return nil
end

function nc:removeObserver(func,event)
    local i = self:observerExists(func,event)
    if i then
        table.remove(self.observers[event],i)
    end
end

function nc:addObserver(func,event)
    if self.observers[event] then
        if not self:observerExists(func,event) then
            table.insert(self.observers[event],func)
        end
    else
        local a = {}
        table.insert(a,func)
        self.observers[event] = a
        local function notifyScript(event)
            for k,v in ipairs(self.observers[event]) do
                v()
            end
        end
        self.center:registerScriptObserver(self.obj,notifyScript,event)
    end
end

function nc:removeAllObservers()
    self.center:removeAllObservers(self.obj)
end

function nc:runTests()
    local function foo1()
        print 'foo1'
    end

    local function foo2()
        print 'foo2'
    end

    local event = 'event_foo'
    -- Add two observers of the same event
    self:addObserver(foo1,event)
    self:addObserver(foo2,event)

    -- Post an notification. Should print two lines ('foo1', 'foo2')
    self:post(event)

    -- Add an existing observer
    self:addObserver(foo1,event)

    -- Remove an observer
    self:removeObserver(foo1,event)
    -- Post an notification. Should only print one line ('foo2')
    self:post(event)

    self:removeAllObservers()
end

nc:runTests()

-- Return package table
return nc

1. line 27, "exists" is not used, I suggest remove it.
2. line 47, "a" is global, I suggest prefix it with 'local'.