Call a function in a script that will do in this script from another one

I have one script. For example:

a = 0
function Increment()
    a += 1
end
another one:
script = ...
scirpt.Increment()

and in the first script a will be 1.
Are there any solutions?

Module-scripts exist?
You can require the module script and be able to use the Increment function in client/server scripts.

local Module = require(game.ReplicatedStorage.IncrementModule)

script.Parent.Text = Module.Increment()
-- script 1
a = 0
function Increment()
    a += 1
end

BindableEvent.Event:Connect(Increment)
-- script 2
BindableEvent:Fire()

Will call Increment() in script 1 from script 2

You have 3 options as far as I can tell, ModuleScripts, BindableInstance (BindableFunctions/BindableEvents) or the global environment (.G), best of luck.

Thank you, but i think _G will call a function in script where function called