Considerations

Module interactions

Let’s say that we have two modules, Foo and Bar. Luau will try to resolve the paths if it can find any require in any scripts. In this case, when you say script.Parent.Bar, Luau will resolve it as: relative to this script, go to my parent and get that script named Bar.

-- Module Foo
local Bar = require(script.Parent.Bar)

local baz1: Bar.Baz = 1     -- not ok
local baz2: Bar.Baz = "foo" -- ok

print(Bar.Quux)         -- ok
print(Bar.FakeProperty) -- not ok

Bar.NewProperty = true -- not ok

-- Module Bar
export type Baz = string

local module = {}

module.Quux = "Hello, world!"

return module

There are some caveats here though. For instance, the require path must be resolvable statically, otherwise Luau cannot accurately type check it.

Cyclic module dependencies

Cyclic module dependencies can cause problems for the type checker. In order to break a module dependency cycle a typecast of the module to any may be used:

local myModule = require(MyModule) :: any