[Meta PR] Convert to TypeScript

.babelrc.js

@@ -2,6 +2,7 @@ const { NODE_ENV } = process.env
 
 module.exports = {
   presets: [
+    '@babel/typescript',
     [
       '@babel/env',
       {

.eslintignore

@@ -3,3 +3,5 @@
 **/server.js
 **/webpack.config*.js
 **/flow-typed/**
+# TODO: figure out a way to lint this using flow instead of typescript
+examples/todos-flow

.eslintrc.js

@@ -1,22 +1,34 @@
 module.exports = {
   extends: 'react-app',
 
+  parser: '@typescript-eslint/parser',
+
+  plugins: ['@typescript-eslint'],
+
   settings: {
     react: {
       version: '16.8'
+    },
+    'import/parsers': {
+      '@typescript-eslint/parser': ['.ts', '.tsx']
+    },
+    'import/resolver': {
+      // use <root>/tsconfig.json
+      typescript: {}
     }
   },
 
   rules: {
-    'jsx-a11y/href-no-hash': 'off'
-  },
-
-  overrides: [
-    {
-      files: 'test/**/*.js',
-      env: {
-        jest: true,
-      },
-    },
-  ],
+    'jsx-a11y/href-no-hash': 'off',
+    'no-unused-vars': 'off',
+    '@typescript-eslint/no-unused-vars': [
+      'error',
+      {
+        vars: 'all',
+        args: 'after-used',
+        ignoreRestSiblings: true,
+        argsIgnorePattern: '^_' // ignore unused variables whose name is '_'
+      }
+    ]
+  }
 }

.gitignore

@@ -1,10 +1,11 @@
-.DS_Store
-*.log
 node_modules
+
+coverage
+
 dist
 lib
 es
-coverage
+types
 
 website/translated_docs
 website/build/

examples/todomvc/src/components/App.spec.js

@@ -4,8 +4,7 @@ import App from './App'
 import Header from '../containers/Header'
 import MainSection from '../containers/MainSection'
 
-
-const setup = propOverrides => {
+const setup = _propOverrides => {
   const renderer = createRenderer()
   renderer.render(<App />)
   const output = renderer.getRenderOutput()
@@ -16,16 +15,16 @@ describe('components', () => {
   describe('Header', () => {
     it('should render', () => {
       const output = setup()
-      const [ header ] = output.props.children
+      const [header] = output.props.children
       expect(header.type).toBe(Header)
     })
   })
-  
+
   describe('Mainsection', () => {
     it('should render', () => {
       const output = setup()
-      const [ , mainSection ] = output.props.children
+      const [, mainSection] = output.props.children
       expect(mainSection.type).toBe(MainSection)
     })
   })
-})
+})

index.d.ts

@@ -211,7 +211,7 @@ export function combineReducers<M extends ReducersMapObject<any, any>>(
  *   dispatched.
  */
 export interface Dispatch<A extends Action = AnyAction> {
-  <T extends A>(action: T): T
+  <T extends A>(action: T, ...extraArgs: any[]): T
 }
 
 /**
@@ -247,15 +247,33 @@ export type Observer<T> = {
   next?(value: T): void
 }
 
+/**
+ * Extend the state
+ *
+ * This is used by store enhancers and store creators to extend state.
+ * If there is no state extension, it just returns the state, as is, otherwise
+ * it returns the state joined with its extension.
+ */
+export type ExtendState<State, Extension> = [Extension] extends [never]
+  ? State
+  : State & Extension
+
 /**
  * A store is an object that holds the application's state tree.
  * There should only be a single store in a Redux app, as the composition
  * happens on the reducer level.
  *
  * @template S The type of state held by this store.
  * @template A the type of actions which may be dispatched by this store.
+ * @template StateExt any extension to state from store enhancers
+ * @template Ext any extensions to the store from store enhancers
  */
-export interface Store<S = any, A extends Action = AnyAction> {
+export interface Store<
+  S = any,
+  A extends Action = AnyAction,
+  StateExt = never,
+  Ext = {}
+> {
   /**
    * Dispatches an action. It is the only way to trigger a state change.
    *
@@ -326,7 +344,9 @@ export interface Store<S = any, A extends Action = AnyAction> {
    *
    * @param nextReducer The reducer for the store to use instead.
    */
-  replaceReducer(nextReducer: Reducer<S, A>): void
+  replaceReducer<NewState, NewActions extends Action>(
+    nextReducer: Reducer<NewState, NewActions>
+  ): Store<ExtendState<NewState, StateExt>, NewActions, StateExt, Ext> & Ext
 
   /**
    * Interoperability point for observable/reactive libraries.
@@ -353,15 +373,15 @@ export type DeepPartial<T> = {
  * @template StateExt State extension that is mixed into the state type.
  */
 export interface StoreCreator {
-  <S, A extends Action, Ext, StateExt>(
+  <S, A extends Action, Ext = {}, StateExt = never>(
     reducer: Reducer<S, A>,
     enhancer?: StoreEnhancer<Ext, StateExt>
-  ): Store<S & StateExt, A> & Ext
-  <S, A extends Action, Ext, StateExt>(
+  ): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
+  <S, A extends Action, Ext = {}, StateExt = never>(
     reducer: Reducer<S, A>,
     preloadedState?: PreloadedState<S>,
     enhancer?: StoreEnhancer<Ext>
-  ): Store<S & StateExt, A> & Ext
+  ): Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
 }
 
 /**
@@ -415,16 +435,17 @@ export const createStore: StoreCreator
  * @template Ext Store extension that is mixed into the Store type.
  * @template StateExt State extension that is mixed into the state type.
  */
-export type StoreEnhancer<Ext = {}, StateExt = {}> = (
-  next: StoreEnhancerStoreCreator
+export type StoreEnhancer<Ext = {}, StateExt = never> = (
+  next: StoreEnhancerStoreCreator<Ext, StateExt>
 ) => StoreEnhancerStoreCreator<Ext, StateExt>
-export type StoreEnhancerStoreCreator<Ext = {}, StateExt = {}> = <
+
+export type StoreEnhancerStoreCreator<Ext = {}, StateExt = never> = <
   S = any,
   A extends Action = AnyAction
 >(
   reducer: Reducer<S, A>,
   preloadedState?: PreloadedState<S>
-) => Store<S & StateExt, A> & Ext
+) => Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext
 
 /* middleware */
 
@@ -667,3 +688,9 @@ export function compose<R>(
 ): (...args: any[]) => R
 
 export function compose<R>(...funcs: Function[]): (...args: any[]) => R
+
+export const __DO_NOT_USE__ActionTypes: {
+  INIT: string
+  REPLACE: string
+  PROBE_UNKNOWN_ACTION: () => string
+}