Type the Redux store

js/store.js

@@ -1,48 +0,0 @@
-import { createStore, applyMiddleware } from "redux";
-import thunk from "redux-thunk";
-import { composeWithDevTools } from "redux-devtools-extension";
-import reducer from "./reducers";
-import mediaMiddleware from "./mediaMiddleware";
-import { merge } from "./utils";
-import { UPDATE_TIME_ELAPSED, STEP_MARQUEE } from "./actionTypes";
-
-const compose = composeWithDevTools({
-  actionsBlacklist: [UPDATE_TIME_ELAPSED, STEP_MARQUEE]
-});
-
-export default function(
-  media,
-  actionEmitter,
-  customMiddlewares = [],
-  stateOverrides,
-  extras
-) {
-  let initialState;
-  if (stateOverrides) {
-    initialState = merge(
-      reducer(undefined, { type: "@@init" }),
-      stateOverrides
-    );
-  }
-
-  // eslint-disable-next-line no-unused-vars
-  const emitterMiddleware = store => next => action => {
-    actionEmitter.trigger(action.type, action);
-    return next(action);
-  };
-
-  return createStore(
-    reducer,
-    initialState,
-    compose(
-      applyMiddleware(
-        ...[
-          thunk.withExtraArgument(extras),
-          mediaMiddleware(media),
-          emitterMiddleware,
-          ...customMiddlewares
-        ].filter(Boolean)
-      )
-    )
-  );
-}

js/store.ts

@@ -0,0 +1,56 @@
+import { createStore, applyMiddleware, DeepPartial } from "redux";
+import thunk from "redux-thunk";
+import { composeWithDevTools } from "redux-devtools-extension";
+import reducer from "./reducers";
+import mediaMiddleware from "./mediaMiddleware";
+import { merge } from "./utils";
+import { UPDATE_TIME_ELAPSED, STEP_MARQUEE } from "./actionTypes";
+import Media from "./media";
+import Emitter from "./emitter";
+import { Extras, MiddlewareStore, Dispatch, Action, AppState } from "./types";
+
+const compose = composeWithDevTools({
+  actionsBlacklist: [UPDATE_TIME_ELAPSED, STEP_MARQUEE]
+});
+
+export default function(
+  media: Media,
+  actionEmitter: Emitter,
+  customMiddlewares = [],
+  stateOverrides: DeepPartial<AppState>,
+  extras: Extras
+) {
+  let initialState;
+  if (stateOverrides) {
+    initialState = merge(
+      reducer(undefined, { type: "@@init" }),
+      stateOverrides
+    );
+  }
+
+  // eslint-disable-next-line no-unused-vars
+  const emitterMiddleware = (store: MiddlewareStore) => (next: Dispatch) => (
+    action: Action
+  ) => {
+    actionEmitter.trigger(action.type, action);
+    return next(action);
+  };
+
+  const enhancer = compose(
+    applyMiddleware(
+      ...[
+        thunk.withExtraArgument(extras),
+        mediaMiddleware(media),
+        emitterMiddleware,
+        ...customMiddlewares
+      ].filter(Boolean)
+    )
+  );
+
+  // The Redux types are a bit confused, and don't realize that passing an
+  // undefined initialState is allowed.
+  const store = initialState
+    ? createStore(reducer, initialState, enhancer)
+    : createStore(reducer, enhancer);
+  return store;
+}