`EventEmitter` in Lua (primarily) for my OOP-y, retained-mode, gamepad-friendly UI library.

eventEmitter.lua

local Object = require 'lib.classic'

local function push (t, ...)
  local pushed = select('#', ...)

  for i = 1, pushed do
    t[t.n + i] = select(i, ...)
  end

  return t.n + pushed
end

local function clean (t, n)
  for i = t.n, n do
    t[i] = nil
  end
end

local EventEmitter = Object:extend()

function EventEmitter:emit(eventName, ...)
  if not self.subscribers then return end
  local subscriptions = self.subscribers[eventName]
  if not subscriptions or #subscriptions == 0 then return end

  for i = 1, #subscriptions do
    local sub = subscriptions[i]
    local ok, message

    if sub.args then
      local n = push(sub.args, ...)
      ok, message = pcall(sub.listener, unpack(sub.args, 1, n))
      clean(sub.args, n)
    else
      ok, message = pcall(sub.listener, ...)
    end

    if not ok then
      log.error(message)
    end
  end
end

function EventEmitter:on(eventName, listener, ...)
  if not self.subscribers then
    self.subscribers = setmetatable({}, { __k = 'kv' })
  end

  if not self.subscribers[eventName] then
    self.subscribers[eventName] = {}
  end

  local newSub = {
    listener = listener,
  }

  local n = select('#', ...)
  if n > 0 then
    newSub.args = { n = n, ... }
  end

  table.insert(self.subscribers[eventName], newSub)
end

return EventEmitter

Updated with very useful bugfix and garbage control from https://gist.github.com/pablomayobre/f90491235e7143bbe9e12aca52c23c13 using techniques from his own https://gist.github.com/pablomayobre/adc1ed058a9ae350df559e2b100949dc.