Add Flow type annotations

.eslintrc

@@ -10,6 +10,10 @@
     "react/jsx-uses-vars": 2,
     "react/react-in-jsx-scope": 2,
 
+    // Disable until Flow supports let and const
+    "no-var": 0,
+    "vars-on-top": 0,
+
     //Temporarirly disabled due to a possible bug in babel-eslint (todomvc example)
     "block-scoped-var": 0,
     // Temporarily disabled for test/* until babel/babel-eslint#33 is resolved

.flowconfig

@@ -0,0 +1,9 @@
+[ignore]
+.*/lib
+.*/test
+
+[include]
+
+[libs]
+
+[options]

src/Store.js

@@ -1,8 +1,16 @@
+/* @flow */
+
 import invariant from 'invariant';
 import isPlainObject from './utils/isPlainObject';
 
+import type { State, Action, Reducer } from './types';
+
 export default class Store {
-  constructor(reducer, initialState) {
+  state: State;
+  reducer: Reducer;
+  listeners: Array<Function>;
+
+  constructor(reducer: Reducer, initialState: State): void {
     invariant(
       typeof reducer === 'function',
       'Expected the reducer to be a function.'
@@ -13,37 +21,37 @@ export default class Store {
     this.replaceReducer(reducer);
   }
 
-  getReducer() {
+  getReducer(): Reducer {
     return this.reducer;
   }
 
-  replaceReducer(nextReducer) {
+  replaceReducer(nextReducer: Reducer): void {
     this.reducer = nextReducer;
     this.dispatch({ type: '@@INIT' });
   }
 
-  dispatch(action) {
+  dispatch(action: Action): Action {
     invariant(
       isPlainObject(action),
       'Actions must be plain objects. Use custom middleware for async actions.'
     );
 
-    const { reducer } = this;
+    var { reducer } = this;
     this.state = reducer(this.state, action);
     this.listeners.forEach(listener => listener());
     return action;
   }
 
-  getState() {
+  getState(): State {
     return this.state;
   }
 
-  subscribe(listener) {
-    const { listeners } = this;
+  subscribe(listener: Function): Function {
+    var { listeners } = this;
     listeners.push(listener);
 
     return function unsubscribe() {
-      const index = listeners.indexOf(listener);
+      var index = listeners.indexOf(listener);
       listeners.splice(index, 1);
     };
   }

src/createStore.js

@@ -1,21 +1,25 @@
-import Store from './Store';
+/* @flow */
+
+import StoreClass from './Store';
 import combineReducers from './utils/combineReducers';
 
+import type { State, Action, Reducer, Dispatch, Store } from './types';
+
 export default function createStore(
-  reducer,
-  initialState
-) {
-  const finalReducer = typeof reducer === 'function' ?
+  reducer: Reducer,
+  initialState: State
+): Store {
+  var finalReducer = typeof reducer === 'function' ?
     reducer :
     combineReducers(reducer);
 
-  const store = new Store(finalReducer, initialState);
+  var store = new StoreClass(finalReducer, initialState);
 
   return {
-    dispatch: ::store.dispatch,
-    subscribe: ::store.subscribe,
-    getState: ::store.getState,
-    getReducer: ::store.getReducer,
-    replaceReducer: ::store.replaceReducer
+    dispatch: store.dispatch.bind(store),
+    subscribe: store.subscribe.bind(store),
+    getState: store.getState.bind(store),
+    getReducer: store.getReducer.bind(store),
+    replaceReducer: store.replaceReducer.bind(store)
   };
 }

src/middleware/thunk.js

@@ -1,5 +1,12 @@
-export default function thunkMiddleware({ dispatch, getState }) {
-  return next => action =>
+/* @flow */
+
+import type { Dispatch, State, Action } from '../types';
+
+type StoreMethods = { dispatch: Dispatch, getState: () => State };
+
+export default function thunkMiddleware(storeMethods: StoreMethods): Dispatch {
+  var { dispatch, getState } = storeMethods;
+  return (next: Dispatch) => (action: Action) =>
     typeof action === 'function' ?
       action(dispatch, getState) :
       next(action);

src/types.js

@@ -0,0 +1,10 @@
+export type State = any;
+export type Action = Object;
+export type IntermediateAction = any;
+export type Dispatch = (a: Action | IntermediateAction) => any;
+export type Reducer<S, A> = (state: S, action: A) => S;
+export type ActionCreator = (...args: any) => Action | IntermediateAction
+export type Middleware = (methods: { dispatch: Dispatch, getState: () => State }) => (next: Dispatch) => Dispatch;
+export type Store = { dispatch: Dispatch, getState: State, subscribe: Function, getReducer: Reducer, replaceReducer: void };
+export type CreateStore = (reducer: Function, initialState: any) => Store;
+export type HigherOrderStore = (next: CreateStore) => CreateStore;

src/utils/applyMiddleware.js

@@ -1,22 +1,28 @@
+/* @flow */
+
 import compose from './compose';
 import composeMiddleware from './composeMiddleware';
 import thunk from '../middleware/thunk';
 
+import type { Middleware, Dispatch, CreateStore } from '../types';
+
 /**
  * Creates a higher-order store that applies middleware to a store's dispatch.
  * Because middleware is potentially asynchronous, this should be the first
  * higher-order store in the composition chain.
  * @param {...Function} ...middlewares
  * @return {Function} A higher-order store
  */
-export default function applyMiddleware(...middlewares) {
-  const finalMiddlewares = middlewares.length ?
+export default function applyMiddleware(
+  ...middlewares: Array<Middleware>
+): Dispatch {
+  var finalMiddlewares = middlewares.length ?
     middlewares :
     [thunk];
 
-  return next => (...args) => {
-    const store = next(...args);
-    const methods = {
+  return (next: CreateStore) => (...args) => {
+    var store = next(...args);
+    var methods = {
       dispatch: store.dispatch,
       getState: store.getState
     };

src/utils/bindActionCreators.js

@@ -1,6 +1,12 @@
+/* @flow */
+
 import mapValues from '../utils/mapValues';
 
-export default function bindActionCreators(actionCreators, dispatch) {
+import type { Dispatch } from '../types';
+
+export default function bindActionCreators(
+  actionCreators: Object, dispatch: Dispatch
+): Object {
   return mapValues(actionCreators, actionCreator =>
     (...args) => dispatch(actionCreator(...args))
   );

src/utils/combineReducers.js

@@ -2,7 +2,9 @@ import mapValues from '../utils/mapValues';
 import pick from '../utils/pick';
 import invariant from 'invariant';
 
-function getErrorMessage(key, action) {
+import type { Action, State, Reducer } from '../types';
+
+function getErrorMessage(key: String, action: Action): String {
   const actionType = action && action.type;
   const actionName = actionType && `"${actionType}"` || 'an action';
   const reducerName = `Reducer "${key}"`;
@@ -21,10 +23,10 @@ function getErrorMessage(key, action) {
   );
 }
 
-export default function combineReducers(reducers) {
+export default function combineReducers(reducers: Object): Reducer {
   const finalReducers = pick(reducers, (val) => typeof val === 'function');
 
-  return function composition(state = {}, action) {
+  return function composition(state: State = {}, action: Action): State {
     return mapValues(finalReducers, (reducer, key) => {
       const newState = reducer(state[key], action);
       invariant(

src/utils/compose.js

@@ -1,8 +1,10 @@
+/* @flow */
+
 /**
  * Composes functions from left to right
  * @param  {...Function} funcs - Functions to compose
  * @return {Function}
  */
-export default function compose(...funcs) {
+export default function compose(...funcs: Array<Function>): Function {
   return funcs.reduceRight((composed, f) => f(composed));
 }

src/utils/createStoreShape.js

@@ -1,4 +1,6 @@
-export default function createStoreShape(PropTypes) {
+/* @flow */
+
+export default function createStoreShape(PropTypes: Object): Object {
   return PropTypes.shape({
     subscribe: PropTypes.func.isRequired,
     dispatch: PropTypes.func.isRequired,

src/utils/identity.js

@@ -1,3 +1,5 @@
-export default function identity(value) {
+/* @flow */
+
+export default function identity<T>(value: T): T {
   return value;
 }

src/utils/isPlainObject.js

@@ -1,3 +1,5 @@
-export default function isPlainObject(obj) {
+/* @flow */
+
+export default function isPlainObject(obj: Object): boolean {
   return obj ? typeof obj === 'object' && Object.getPrototypeOf(obj) === Object.prototype : false;
 }

src/utils/mapValues.js

@@ -1,4 +1,6 @@
-export default function mapValues(obj, fn) {
+/* @flow */
+
+export default function mapValues(obj: Object, fn: Function): Object {
   return Object.keys(obj).reduce((result, key) => {
     result[key] = fn(obj[key], key);
     return result;

src/utils/pick.js

@@ -1,4 +1,6 @@
-export default function pick(obj, fn) {
+/* @flow */
+
+export default function pick(obj: Object, fn: Function): Object {
   return Object.keys(obj).reduce((result, key) => {
     if (fn(obj[key])) {
       result[key] = obj[key];

src/utils/shallowEqual.js

@@ -1,18 +1,20 @@
-export default function shallowEqual(objA, objB) {
+/* @flow */
+
+export default function shallowEqual(objA: Object, objB: Object): boolean {
   if (objA === objB) {
     return true;
   }
 
-  const keysA = Object.keys(objA);
-  const keysB = Object.keys(objB);
+  var keysA = Object.keys(objA);
+  var keysB = Object.keys(objB);
 
   if (keysA.length !== keysB.length) {
     return false;
   }
 
   // Test for A's keys different from B.
-  const hasOwn = Object.prototype.hasOwnProperty;
-  for (let i = 0; i < keysA.length; i++) {
+  var hasOwn = Object.prototype.hasOwnProperty;
+  for (var i = 0; i < keysA.length; i++) {
     if (!hasOwn.call(objB, keysA[i]) ||
         objA[keysA[i]] !== objB[keysA[i]]) {
       return false;

src/utils/shallowEqualScalar.js

@@ -1,4 +1,6 @@
-export default function shallowEqualScalar(objA, objB) {
+/* @flow */
+
+export default function shallowEqualScalar(objA: Object, objB: Object): boolean {
   if (objA === objB) {
     return true;
   }
@@ -8,22 +10,22 @@ export default function shallowEqualScalar(objA, objB) {
     return false;
   }
 
-  const keysA = Object.keys(objA);
-  const keysB = Object.keys(objB);
+  var keysA = Object.keys(objA);
+  var keysB = Object.keys(objB);
 
   if (keysA.length !== keysB.length) {
     return false;
   }
 
   // Test for A's keys different from B.
-  const hasOwn = Object.prototype.hasOwnProperty;
-  for (let i = 0; i < keysA.length; i++) {
+  var hasOwn = Object.prototype.hasOwnProperty;
+  for (var i = 0; i < keysA.length; i++) {
     if (!hasOwn.call(objB, keysA[i])) {
       return false;
     }
 
-    const valA = objA[keysA[i]];
-    const valB = objB[keysA[i]];
+    var valA = objA[keysA[i]];
+    var valB = objB[keysA[i]];
 
     if (valA !== valB || typeof valA === 'object' || typeof valB === 'object') {
       return false;