Properties and Attributes

Making experiences interactive often means manipulating object properties and attributes:

• Properties are part of the object class. For example, the BasePart.Anchored property controls physics for the part. In a track and field experience, you might want to anchor a discus or javelin the instant it lands so that players have a visual indicator of how far it traveled.

• Attributes are essentially custom properties that you define. For example, the Plant reference project uses attributes to set the purchase price for seeds and the maximum plant size that a pot can hold.

Replication Order

Before you begin retrieving and manipulating objects, you must have an understanding of replication order.

The Roblox engine doesn't guarantee the order in which objects are replicated from the server to the client, which makes the Instance:WaitForChild() method essential for accessing objects in client scripts, particularly objects in the Workspace. Still, some aspects of the process are predictable:

1. The client loads the contents of ReplicatedFirst, such as a loading screen, assets, and scripts.

2. LocalScripts (and Scripts with a RunContext of Client) in ReplicatedFirst run. These scripts can safely get objects from ReplicatedFirst without using WaitForChild():

   -- Safe
   local ReplicatedFirst = game:GetService("ReplicatedFirst")
   local LoadingScreen = require(ReplicatedFirst.LoadingScreen)

   These scripts can't safely get objects from other services, because they might not have loaded yet:

   -- Not safe
   local ReplicatedStorage = game:GetService("ReplicatedStorage")
   local PickupManager = require(ReplicatedStorage.PickupManager)

   You can use WaitForChild() in these scripts to get objects from other services, but doing so largely negates the benefits of using ReplicatedFirst.

3. The client continues loading the rest of the experience.

4. When it finishes, the game.Loaded event fires and game:IsLoaded() returns true.

5. LocalScripts in StarterPlayerScripts run, as well as client Scripts in ReplicatedStorage. These scripts can safely get objects from StarterPlayerScripts and ReplicatedStorage without using WaitForChild().

6. The player's Character model spawns in the experience.

7. LocalScripts in StarterCharacterScripts run.

If your experience uses instance streaming (Workspace.StreamingEnabled), some or most objects might not have loaded into the workspace, so using WaitForChild() to access workspace objects becomes an even more important safety measure. In particular, see Streaming In and Per-Model Streaming Controls for additional information on loading and tuning streaming behavior.

Getting Objects

The first step to modifying object properties and attributes is to get a reference to the object. The simplest solution is to make the script a child of the object in the Explorer and use script.Parent to reference the object.

local sign = script.Parent

The more universal solution is to get the object from a service using methods like Instance:FindFirstChild() or Instance:WaitForChild().

local ReplicatedStorage = game:GetService("ReplicatedStorage")

local signsFolder = ReplicatedStorage:WaitForChild("Signs")
local sign = signsFolder:WaitForChild("InteractiveSign")

Modifying Properties

Properties are straightforward to access — just use a . after the object reference — although if you're working with a model, you might need to choose an individual part rather than the model itself.

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local chair = ReplicatedStorage:WaitForChild("Chair")

chair.LeftArmRest.Size = Vector3.new(10, 1, 10)

Creating Attributes

Although you can create attributes programmatically, the more common solution is to create them with default values in the Studio user interface. Then you can use scripts to modify their values in response to player actions.

For information on creating attributes in Studio, see Instance Attributes.

Setting Attributes

To modify an attribute's value, call Instance:SetAttribute() with a name and value.

Create or Modify Attribute
local cabbage = script.Parent

cabbage:SetAttribute("Harvestable", true)

If the attribute doesn't already exist, this method creates it.

Getting Attribute Values

To get the value of one existing attribute, call Instance:GetAttribute() on the instance.

Get Attribute Value
local cabbage = script.Parent

cabbage:SetAttribute("Harvestable", true)

local isHarvestable = cabbage:GetAttribute("Harvestable")
print(isHarvestable) --> true

Similarly, you can get all attributes by calling Instance:GetAttributes(). This method returns a dictionary of key-value pairs.

Get All Attributes
local cabbage = script.Parent

local cabbageAttributes = cabbage:GetAttributes()

print(cabbageAttributes.GrowthRate) --> 2

for k, v in cabbageAttributes do
	print(k, v)
end

Deleting Attributes

To delete an attribute, set its value to nil.

Delete Attribute
local cabbage = script.Parent

cabbage:SetAttribute("GrowthRate", nil)

Detecting Changes

There are several ways to listen for changes to properties and attributes:

• The Instance.Changed event listens for changes to any property (including attributes) and passes the name of the changed property as a parameter.

  In the case of attribute changes, Instance.Changed fires and passes the string "Attributes", which lets you ignore the event, but isn't especially useful otherwise.

• The Instance.AttributeChanged event listens for changes to any attribute and passes the name of the changed attribute as a parameter.

• The Instance:GetPropertyChangedSignal() method lets you listen for changes to one property and passes no parameters.

• The Instance:GetAttributeChangedSignal() method lets you listen for changes to one attribute and passes no parameters.

Due to the minimal information that these events and methods pass as parameters, all of them are a good fit for anonymous functions, particularly Instance:GetPropertyChangedSignal() and Instance:GetAttributeChangedSignal(). To learn more about anonymous functions and working with events, see Events.

Listen for Changes
local cabbage = script.Parent

-- Local functions
local function onAnyPropertyChange(property)
	-- Ignore changes to attributes
	if property ~= "Attributes" then
		print(property) --> Name
		print(cabbage[property]) --> Cabbage1
	end
end

local function onAnyAttributeChange(attribute)
	print(attribute) --> Grow, GrowthRate
	print(cabbage:GetAttribute(attribute)) --> false, 3
end

-- Listen for changes and connect to local functions
cabbage.Changed:Connect(onAnyPropertyChange)
cabbage.AttributeChanged:Connect(onAnyAttributeChange)

-- Listen for changes and connect to anonymous functions
cabbage:GetPropertyChangedSignal("Name"):Connect(function()
	print(cabbage.Name) --> Cabbage1
end)
cabbage:GetAttributeChangedSignal("GrowthRate"):Connect(function()
	print(cabbage:GetAttribute("GrowthRate")) --> 3
end)

-- Fires Changed and GetPropertyChangedSignal()
cabbage.Name = "Cabbage1"

-- Fires Changed and AttributeChanged
cabbage:SetAttribute("Grow", false)

-- Fires Changed, AttributeChanged, and GetAttributeChangedSignal()
cabbage:SetAttribute("GrowthRate", 3)