# Cleanup

Sometimes you may need to do some cleanup when destroying a component or after
a side-effect from a source update. Vide provides a function `cleanup()` which
is used to register a cleanup callback for the next time the reactive scope
it is called in re-runs.

```lua
locla mount = vide.mount
local source = vide.source
local cleanup = vide.cleanup

local function Timer()
    local count = source(0)

    local con = game:GetService("RunService").Heartbeat:Connect(function(dt)
        count(count() + dt)
    end)

    cleanup(function()
        con:Disconnect()
    end)

    return create "TextButton" {
        Position = UDim2.fromOffset(300, 300),
        Size = UDim2.fromOffset(200, 50),

        Text = function()
            return "seconds: " .. math.floor(count())
        end,
    }
end

local unmount = mount(Timer)

unmount() -- all registered cleanups are ran, heartbeat connection stopped
```

In the above example, this allows us to disconnect the heartbeat connection
when the timer component is destroyed, whether that is from unmounting the app
or if it is dynamically created by a control-flow function, which will be
covered next.

On a related note: the reason why `mount()` is used to create your app, is so
that any top-level components that need to be cleaned up, can be cleaned up
when the app is later unmounted, since `mount()` runs in a reactive-scope to
track `cleanup()` calls. Vide's entire reactive system is independent from the
life-time of instances; instances are just a side-effect of the reactive system.