Debounce – When and Why

5 min

A debounce system is a set of code that keeps a function from running too many times. It comes from the idea of mechanical switch bounce, where a pushed switch bounces and creates multiple signals. In Roblox, this problem occurs mainly with the BasePart/Touched event which fires every time a player’s body part contacts the detection part.

Common Case

Assume you want to build a hazardous trap part on the floor that causes 10 damage when touched. Code in a Script attached to the part may look like this:

			
				Damage Player - No Debounce
			
				Expected Output
			
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			local trap = script.Parent

local function damagePlayer(otherPart)
	local partParent = otherPart.Parent
	local humanoid = partParent:FindFirstChildWhichIsA("Humanoid")

	if humanoid then
		humanoid.Health = humanoid.Health - 10
		print("OUCH!")
	end
end

trap.Touched:Connect(damagePlayer)
		
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The problem is that — because of how the physics engine handles collisions — the code will trigger multiple near-simultaneous events and cause more damage than intended.

To solve the problem, a debounce system can be included with a reset time as follows:

			
				Damage Player - Debounce Variable
			
				Expected Output
			
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			local trap = script.Parent

local RESET_SECONDS = 1
local isTouched = false  -- Declare debounce variable

local function damagePlayer(otherPart)
	local partParent = otherPart.Parent
	local humanoid = partParent:FindFirstChildWhichIsA("Humanoid")

	if humanoid then
		if not isTouched then  -- Check that debounce variable is not true
			isTouched = true  -- Set variable to true
			humanoid.Health = humanoid.Health - 10
			print("OUCH!")
			wait(RESET_SECONDS)  -- Wait for reset time duration
			isTouched = false  -- Reset variable to false
		end
	end
end

trap.Touched:Connect(damagePlayer)
		
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Alternatively to a local variable in the script, debounce can be managed by an articles/instance attributes|attribute directly on the object. For instance, the code below checks for a boolean IsTouched attribute on the trap part itself:

			
				Damage Player - Debounce Attribute
			
				Expected Output
			
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			local trap = script.Parent

local RESET_SECONDS = 1

local function damagePlayer(otherPart)
	local partParent = otherPart.Parent
	local humanoid = partParent:FindFirstChildWhichIsA("Humanoid")

	if humanoid then
		if not trap:GetAttribute("IsTouched") then  -- Check for non-existence of attribute
			trap:SetAttribute("IsTouched", true)  -- Set attribute to true
			humanoid.Health = humanoid.Health - 10
			print("OUCH!")
			wait(RESET_SECONDS)  -- Wait for reset time duration
			trap:SetAttribute("IsTouched", nil)  -- Remove attribute
		end
	end
end

trap.Touched:Connect(damagePlayer)
		
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Other Uses

Beyond BasePart/Touched, debounce is useful for:

Preventing “button mashing” where a player might press an on-screen UI button repeatedly, before the button’s action has a chance to fully resolve.
Limiting how quickly a player can fire a weapon like a rocket launcher, effectively creating a “reload” time for the launcher before another rocket can be fired.
Preventing cumulative stacking of Tween|Tweens before the current tween has resolved.

Tags:

debounce
event
trigger

Debounce – When and Why

Debounce – When and Why

Common Case

Other Uses

Related Articles

Detecting Collisions

Handling Events