Event

Overview

Events are used to implement necessary functions for various situations that occur within the game (such as entering, collisions, etc.).

Linking a Function to an Event

Use :Connect() to link a function to an event.

local Part = script.Parent

local function OnTouched(otherPart)
  print("otherPart : ", otherPart.Name)
end
Part.Touched:Connect(OnTouched)

Unlinking a Function from an Event

If you store the returned value in a variable when you use :Connect() to link a function to an event, you can unlink the function from the event when it is no longer needed.

local Part = script.Parent
local Connection = nil

local function OnTouched(otherPart)
    local partParent = otherPart.Parent
    local humanoid = partParent:FindFirstChild("Humanoid")
 
    if humanoid then
        if Connection ~= nil then
            Connection:Disconnect()	
        end
    end
end
Connection = Part.Touched:Connect(OnTouched)

Waiting for an Event

Using Wait() blocks the current thread until the signal fires once, then returns the arguments that were passed when it fired. The examples below show how to use those return values or chain waits in more involved flows.

When a player joins, wait for their character to be ready, then initialize Humanoid (Server)

local Players = game:GetService("Players")

local function OnPlayerAdded(player)
    local character = player.Character or player.CharacterAdded:Wait()
    local humanoid = character:WaitForChild("Humanoid")
    humanoid.WalkSpeed = 16
end
Players.PlayerAdded:Connect(OnPlayerAdded)

Use the instance returned by Wait() for follow-up work

local Folder = workspace:FindFirstChild("SpawnContainer")
local AddedChild = Folder.ChildAdded:Wait()
local Nested = AddedChild:FindFirstChild("Config")

if Nested and Nested:IsA("ModuleScript") then
    -- load module or other follow-up logic
end

Signals that return multiple values: AncestryChanged passes (child, parent)

local Part = workspace:FindFirstChild("MovingPart")
Part.Parent = nil
Part.Parent = workspace.TargetFolder

local Child, NewParent = Part.AncestryChanged:Wait()

if NewParent then
    print("New Parent: ", NewParent:GetFullName())
end

Wait once for server-sent data via RemoteEvent, then run logic (Client)

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local RemoteEvent = ReplicatedStorage:FindFirstChild("SessionReady")

if RemoteEvent then
    local sessionId, startTime = RemoteEvent.OnClientEvent:Wait()
    -- use sessionId, startTime for UI update or game logic
end

Commonly Used Events

Collision Events

Detects objects that collide with an object to which the event is linked. (For example: Detecting characters that touch a Kill Part)

local Part = script.Parent
local Connection = nil

local function OnTouched(otherPart)
    local partParent = otherPart.Parent
    local humanoid = partParent:FindFirstChild("Humanoid")
 
    if humanoid then
        if Connection ~= nil then
            Connection:Disconnect()	
        end
    end
end
Connection = Part.Touched:Connect(OnTouched)

Detects objects that exit the area (collision range) of the object to which the event is linked. (For example: Escaping from a trap floor)

local function OnTouchEnded(otherPart)
    print("TouchEnded : ", otherPart.Name)
end
part.TouchEnded:Connect(OnTouchEnded)

Update Events

An event that is called every frame. (For example: Timer calculations, object movement, physics operations)

local RunService = game:GetService("RunService")
local Timer = 0

local function UpdateEvent(deltaTime)
    Timer = Timer + deltaTime
    
    if Timer >= 3 then
        Timer = 0
        print("Reset!)
    end
end
RunService.Heartbeat:Connect(UpdateEvent)

Player Join/Leave Events

An event that detects players who join the game.

local Players = game:GetService("Players")

local function EnterPlayer(player)
    print("EnterPlayer : ", player.Name)
end
Players.PlayerAdded:Connect(EnterPlayer)

An event that detects players who leave the game.

local Players = game:GetService("Players")

local function LeavePlayer(player)
    print("LeavePlayer : ", player.Name)
end
Players.PlayerRemoving:Connect(LeavePlayer) 

Character Spawn/Death Events

These are events that detect when a character is spawned or when a character dies.

local Players = game:GetService("Players")

local function EnterPlayer(player)
    -- Spawn
    local function SpawnCharacter(character)    
        local humanoid = character:WaitForChild("Humanoid")
        
        -- Die
        local function DeathCharacter()
            print(player.Name, "Die!")
        end
        humanoid.Died:Connect(DeathCharacter)
    end
    player.CharacterAdded:Connect(SpawnCharacter)
end
Players.PlayerAdded:Connect(EnterPlayer)

Button Click Events

An event that is triggered when a button is clicked.

local ScreenGui = script.Parent
local Button = ScreenGui.TextButton

local function OnActivated()
    print("Activated")
end
Button.Activated:Connect(OnActivated)