Add extra argument to thunk middleware

src/init.lua

@@ -4,6 +4,7 @@ local combineReducers = require(script.combineReducers)
 local makeActionCreator = require(script.makeActionCreator)
 local loggerMiddleware = require(script.loggerMiddleware)
 local thunkMiddleware = require(script.thunkMiddleware)
+local makeThunkMiddleware = require(script.makeThunkMiddleware)
 
 return {
 	Store = Store,
@@ -12,4 +13,5 @@ return {
 	makeActionCreator = makeActionCreator,
 	loggerMiddleware = loggerMiddleware.middleware,
 	thunkMiddleware = thunkMiddleware,
+	makeThunkMiddleware = makeThunkMiddleware,
 }

src/makeThunkMiddleware.lua

@@ -0,0 +1,40 @@
+--[[
+	A middleware that allows for functions to be dispatched with an extra
+	argument for convenience. Functions will receive two arguments:
+	the store itself and the extra argument provided initially to makeThunkMiddleware.
+
+	This middleware consumes the function; middleware further down the chain
+	will not receive it.
+]]
+local function tracebackReporter(message)
+	return debug.traceback(message)
+end
+
+local function makeThunkMiddleware(extraArgument)
+	local function thunkMiddleware(nextDispatch, store)
+		return function(action)
+			if typeof(action) == "function" then
+				local ok, result = xpcall(function()
+					return action(store, extraArgument)
+				end, tracebackReporter)
+
+				if not ok then
+					-- report the error and move on so it's non-fatal app
+					store._errorReporter.reportReducerError(store:getState(), action, {
+						message = "Caught error in thunk",
+						thrownValue = result,
+					})
+					return nil
+				end
+
+				return result
+			end
+
+			return nextDispatch(action)
+		end
+	end
+
+	return thunkMiddleware
+end
+
+return makeThunkMiddleware

src/thunkMiddleware.lua

@@ -4,31 +4,6 @@
 	This middleware consumes the function; middleware further down the chain
 	will not receive it.
 ]]
-local function tracebackReporter(message)
-	return debug.traceback(message)
-end
+local makeThunkMiddleware = require(script.Parent.makeThunkMiddleware)
 
-local function thunkMiddleware(nextDispatch, store)
-	return function(action)
-		if typeof(action) == "function" then
-			local ok, result = xpcall(function()
-				return action(store)
-			end, tracebackReporter)
-
-			if not ok then
-				-- report the error and move on so it's non-fatal app
-				store._errorReporter.reportReducerError(store:getState(), action, {
-					message = "Caught error in thunk",
-					thrownValue = result,
-				})
-				return nil
-			end
-
-			return result
-		end
-
-		return nextDispatch(action)
-	end
-end
-
-return thunkMiddleware
+return makeThunkMiddleware(nil) -- no extra argument

src/thunkMiddleware.spec.lua

@@ -1,6 +1,7 @@
 return function()
 	local Store = require(script.Parent.Store)
 	local thunkMiddleware = require(script.Parent.thunkMiddleware)
+	local makeThunkMiddleware = require(script.Parent.makeThunkMiddleware)
 
 	it("should dispatch thunks", function()
 		local function reducer(state, action)
@@ -117,4 +118,25 @@ return function()
 		store:dispatch(safeThunk)
 		expect(ranSafeThunk).to.equal(true)
 	end)
+
+	it("should send extra argument to thunks when provided", function()
+		local function reducer(state, action)
+			return state
+		end
+
+		local myExtraArg = { What = "MyExtraArg" }
+		local store = Store.new(reducer, {}, { makeThunkMiddleware(myExtraArg) })
+		local thunkCount = 0
+		local extraArgParam = nil
+
+		local function thunk(_store, extraArg)
+			thunkCount = thunkCount + 1
+			extraArgParam = extraArg
+		end
+
+		store:dispatch(thunk)
+
+		expect(thunkCount).to.equal(1)
+		expect(extraArgParam).to.equal(myExtraArg)
+	end)
 end