#Lifecycle

Two keywords run code at the edges of a tree's life.

#ready

ready runs after the instance exists and the root is parented.

{
    ClassName = "Frame",
    Size = UDim2.fromOffset(300, 200),

    ready(function(self)
        print(self.Name, self.AbsoluteSize)
    end),
}

Because the root is already parented, measurements like AbsoluteSize are real by the time your callback runs.

Callbacks run deepest first, climbing the tree. A child is fully set up before its parent's ready runs, so a parent can rely on its children.

Title -> Panel -> ScreenGui

#cleanup

cleanup runs when the tree is torn down, before anything is disconnected or destroyed - so the instance is still usable.

cleanup(function(self)
    print("releasing", self.Name)
end),

#The useful form

After the instance and the vision, ready hands you a third argument: a function that registers cleanup for that node, for that mount. This is the form you will reach for most, because it puts a connection and its disconnect in the same place:

ready(function(self, _, cleanup)
    local Connection = Workspace.ChildAdded:Connect(Handler)

    cleanup(function()
        Connection:Disconnect()
    end)
end),

No bookkeeping table, no remembering to tidy up somewhere else.

#Ordering

Cleanups run deepest first across nodes, matching ready. Within a single node they run last registered first, so anything you set up in ready is released before the cleanup you declared in the table.

#What Cleanup does

Interface:Cleanup()

1. runs cleanup callbacks, deepest first
2. cancels any animation driving this tree
3. disconnects every connection
4. destroys the instances

What it does not do is throw away your values. That is the next page.

#Next

Sleeping and cloning.