Lua Academy · Lesson

Event Systems in Lua

Build a lightweight event dispatcher with callbacks stored in tables.

Event Systems in Lua is a free Lua Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Lua Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Why Event Systems?

An event system decouples producers (things that fire events) from consumers (things that react). In Lua, it is easily built with tables of callback functions.

Simple Event Dispatcher

A dispatcher stores lists of listeners keyed by event name.

local EventEmitter = {}
EventEmitter.__index = EventEmitter

function EventEmitter.new()
  return setmetatable({_listeners = {}}, EventEmitter)
end

function EventEmitter:on(event, fn)
  self._listeners[event] = self._listeners[event] or {}
  table.insert(self._listeners[event], fn)
end

function EventEmitter:emit(event, ...)
  for _, fn in ipairs(self._listeners[event] or {}) do
    fn(...)
  end
end

Using the Dispatcher

Subscribe to events with :on and fire them with :emit.

local bus = EventEmitter.new()
bus:on("playerHit", function(player, damage)
  player.hp = player.hp - damage
  print(player.name, "took", damage, "damage")
end)
bus:emit("playerHit", {name="Alice", hp=100}, 15)

One-Time Listeners

A :once method wraps the callback to deregister itself after the first call.

function EventEmitter:once(event, fn)
  local wrapper
  wrapper = function(...)
    self:off(event, wrapper)
    fn(...)
  end
  self:on(event, wrapper)
end

Removing Listeners

An :off method removes a specific listener by reference.

function EventEmitter:off(event, fn)
  local list = self._listeners[event]
  if not list then return end
  for i, f in ipairs(list) do
    if f == fn then table.remove(list, i); return end
  end
end

Priority Queues for Events

Add a priority field to each listener. Sort the list on registration so high-priority handlers run first.

Async Event Queue

Instead of calling listeners immediately, push events into a queue and process them each frame/tick.

local queue = {}
local function postEvent(event, data)
  queue[#queue+1] = {event=event, data=data}
end
local function processEvents()
  local current = queue
  queue = {}
  for _, e in ipairs(current) do
    bus:emit(e.event, e.data)
  end
end

Preventing Modification During Emit

When emitting, iterate over a copy of the listener list so that adding/removing during emission does not cause bugs.

Namespaced Events

Use dotted event names ("player.damaged", "player.healed") to organize events by system.

Weak Listener Tables

Use weak-value listener tables so that if a subscriber object is GC'd, its listener is automatically removed — preventing leaks in long-running games.

Game Loop Integration

Integrate the event system with the game loop: input events → logic events → render events, processed in order each frame.

Event System Question

What is the main benefit of an event system?

Recap: Event Systems

Lua event systems use a table of named listener lists. Implement on, emit, off, and once for a complete dispatcher. Use async queues and weak tables in production games.

Frequently asked questions

Is the “Event Systems in Lua” lesson free?

Yes — the full text of “Event Systems in Lua” is free to read here on the web, and the Lua Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Lua Academy course, upgrade to CoddyKit PRO.

What will I learn in “Event Systems in Lua”?

Build a lightweight event dispatcher with callbacks stored in tables. You practise Lua Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Lua Academy?

No prior experience is required. Lua Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Event Systems in Lua” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Lua Academy lesson?

Yes. Every Lua Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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