Add TypeScript definitions

index.d.ts

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+/**
+ * An *action* is a plain object that represents an intention to change the
+ * state. Actions are the only way to get data into the store. Any data,
+ * whether from UI events, network callbacks, or other sources such as
+ * WebSockets needs to eventually be dispatched as actions.
+ *
+ * Actions must have a `type` field that indicates the type of action being
+ * performed. Types can be defined as constants and imported from another
+ * module. It’s better to use strings for `type` than Symbols because strings
+ * are serializable.
+ *
+ * Other than `type`, the structure of an action object is really up to you.
+ * If you’re interested, check out Flux Standard Action for recommendations on
+ * how actions should be constructed.
+ */
+export interface Action {
+  type: any;
+}
+
+
+/* reducers */
+
+/**
+ * A *reducer* (also called a *reducing function*) is a function that accepts
+ * an accumulation and a value and returns a new accumulation. They are used
+ * to reduce a collection of values down to a single value
+ *
+ * Reducers are not unique to Redux—they are a fundamental concept in
+ * functional programming.  Even most non-functional languages, like
+ * JavaScript, have a built-in API for reducing. In JavaScript, it's
+ * `Array.prototype.reduce()`.
+ *
+ * In Redux, the accumulated value is the state object, and the values being
+ * accumulated are actions. Reducers calculate a new state given the previous
+ * state and an action. They must be *pure functions*—functions that return
+ * the exact same output for given inputs. They should also be free of
+ * side-effects. This is what enables exciting features like hot reloading and
+ * time travel.
+ *
+ * Reducers are the most important concept in Redux.
+ *
+ * *Do not put API calls into reducers.*
+ *
+ * @template S State object type.
+ */
+export type Reducer<S> = <A extends Action>(state: S, action: A) => S;
+
+/**
+ * Object whose values correspond to different reducer functions.
+ */
+export interface ReducersMapObject {
+  [key: string]: Reducer<any>;
+}
+
+/**
+ * Turns an object whose values are different reducer functions, into a single
+ * reducer function. It will call every child reducer, and gather their results
+ * into a single state object, whose keys correspond to the keys of the passed
+ * reducer functions.
+ *
+ * @template S Combined state object type.
+ *
+ * @param reducers An object whose values correspond to different reducer
+ *   functions that need to be combined into one. One handy way to obtain it
+ *   is to use ES6 `import * as reducers` syntax. The reducers may never
+ *   return undefined for any action. Instead, they should return their
+ *   initial state if the state passed to them was undefined, and the current
+ *   state for any unrecognized action.
+ *
+ * @returns A reducer function that invokes every reducer inside the passed
+ *   object, and builds a state object with the same shape.
+ */
+export function combineReducers<S>(reducers: ReducersMapObject): Reducer<S>;
+
+
+/* store */
+
+/**
+ * A *dispatching function* (or simply *dispatch function*) is a function that
+ * accepts an action or an async action; it then may or may not dispatch one
+ * or more actions to the store.
+ *
+ * We must distinguish between dispatching functions in general and the base
+ * `dispatch` function provided by the store instance without any middleware.
+ *
+ * The base dispatch function *always* synchronously sends an action to the
+ * store’s reducer, along with the previous state returned by the store, to
+ * calculate a new state. It expects actions to be plain objects ready to be
+ * consumed by the reducer.
+ *
+ * Middleware wraps the base dispatch function. It allows the dispatch
+ * function to handle async actions in addition to actions. Middleware may
+ * transform, delay, ignore, or otherwise interpret actions or async actions
+ * before passing them to the next middleware.
+ */
+export type Dispatch = (action: any) => any;
+
+/**
+ * Function to remove listener added by `Store.subscribe()`.
+ */
+export interface Unsubscribe {
+  (): void;
+}
+
+/**
+ * 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 State object type.
+ */
+export interface Store<S> {
+  /**
+   * Dispatches an action. It is the only way to trigger a state change.
+   *
+   * The `reducer` function, used to create the store, will be called with the
+   * current state tree and the given `action`. Its return value will be
+   * considered the **next** state of the tree, and the change listeners will
+   * be notified.
+   *
+   * The base implementation only supports plain object actions. If you want
+   * to dispatch a Promise, an Observable, a thunk, or something else, you
+   * need to wrap your store creating function into the corresponding
+   * middleware. For example, see the documentation for the `redux-thunk`
+   * package. Even the middleware will eventually dispatch plain object
+   * actions using this method.
+   *
+   * @param action A plain object representing “what changed”. It is a good
+   *   idea to keep actions serializable so you can record and replay user
+   *   sessions, or use the time travelling `redux-devtools`. An action must
+   *   have a `type` property which may not be `undefined`. It is a good idea
+   *   to use string constants for action types.
+   *
+   * @returns For convenience, the same action object you dispatched.
+   *
+   * Note that, if you use a custom middleware, it may wrap `dispatch()` to
+   * return something else (for example, a Promise you can await).
+   */
+  dispatch: Dispatch;
+
+  /**
+   * Reads the state tree managed by the store.
+   *
+   * @returns The current state tree of your application.
+   */
+  getState(): S;
+
+  /**
+   * Adds a change listener. It will be called any time an action is
+   * dispatched, and some part of the state tree may potentially have changed.
+   * You may then call `getState()` to read the current state tree inside the
+   * callback.
+   *
+   * You may call `dispatch()` from a change listener, with the following
+   * caveats:
+   *
+   * 1. The subscriptions are snapshotted just before every `dispatch()` call.
+   * If you subscribe or unsubscribe while the listeners are being invoked,
+   * this will not have any effect on the `dispatch()` that is currently in
+   * progress. However, the next `dispatch()` call, whether nested or not,
+   * will use a more recent snapshot of the subscription list.
+   *
+   * 2. The listener should not expect to see all states changes, as the state
+   * might have been updated multiple times during a nested `dispatch()` before
+   * the listener is called. It is, however, guaranteed that all subscribers
+   * registered before the `dispatch()` started will be called with the latest
+   * state by the time it exits.
+   *
+   * @param listener A callback to be invoked on every dispatch.
+   * @returns A function to remove this change listener.
+   */
+  subscribe(listener: () => void): Unsubscribe;
+
+  /**
+   * Replaces the reducer currently used by the store to calculate the state.
+   *
+   * You might need this if your app implements code splitting and you want to
+   * load some of the reducers dynamically. You might also need this if you
+   * implement a hot reloading mechanism for Redux.
+   *
+   * @param nextReducer The reducer for the store to use instead.
+   */
+  replaceReducer(nextReducer: Reducer<S>): void;
+}
+
+/**
+ * A store creator is a function that creates a Redux store. Like with
+ * dispatching function, we must distinguish the base store creator,
+ * `createStore(reducer, initialState)` exported from the Redux package, from
+ * store creators that are returned from the store enhancers.
+ *
+ * @template S State object type.
+ */
+export interface StoreCreator {
+  <S>(reducer: Reducer<S>, enhancer?: StoreEnhancer): Store<S>;
+  <S>(reducer: Reducer<S>, initialState: S,
+      enhancer?: StoreEnhancer): Store<S>;
+}
+
+/**
+ * A store enhancer is a higher-order function that composes a store creator
+ * to return a new, enhanced store creator. This is similar to middleware in
+ * that it allows you to alter the store interface in a composable way.
+ *
+ * Store enhancers are much the same concept as higher-order components in
+ * React, which are also occasionally called “component enhancers”.
+ *
+ * Because a store is not an instance, but rather a plain-object collection of
+ * functions, copies can be easily created and modified without mutating the
+ * original store. There is an example in `compose` documentation
+ * demonstrating that.
+ *
+ * Most likely you’ll never write a store enhancer, but you may use the one
+ * provided by the developer tools. It is what makes time travel possible
+ * without the app being aware it is happening. Amusingly, the Redux
+ * middleware implementation is itself a store enhancer.
+ */
+export type StoreEnhancer = (next: StoreCreator) => StoreCreator;
+
+/**
+ * Creates a Redux store that holds the state tree.
+ * The only way to change the data in the store is to call `dispatch()` on it.
+ *
+ * There should only be a single store in your app. To specify how different
+ * parts of the state tree respond to actions, you may combine several
+ * reducers
+ * into a single reducer function by using `combineReducers`.
+ *
+ * @template S State object type.
+ *
+ * @param reducer A function that returns the next state tree, given the
+ *   current state tree and the action to handle.
+ *
+ * @param [initialState] The initial state. You may optionally specify it to
+ *   hydrate the state from the server in universal apps, or to restore a
+ *   previously serialized user session. If you use `combineReducers` to
+ *   produce the root reducer function, this must be an object with the same
+ *   shape as `combineReducers` keys.
+ *
+ * @param [enhancer] The store enhancer. You may optionally specify it to
+ *   enhance the store with third-party capabilities such as middleware, time
+ *   travel, persistence, etc. The only store enhancer that ships with Redux
+ *   is `applyMiddleware()`.
+ *
+ * @returns A Redux store that lets you read the state, dispatch actions and
+ *   subscribe to changes.
+ */
+export const createStore: StoreCreator;
+
+
+/* middleware */
+
+export interface MiddlewareAPI<S> {
+  dispatch: Dispatch;
+  getState(): S;
+}
+
+/**
+ * A middleware is a higher-order function that composes a dispatch function
+ * to return a new dispatch function. It often turns async actions into
+ * actions.
+ *
+ * Middleware is composable using function composition. It is useful for
+ * logging actions, performing side effects like routing, or turning an
+ * asynchronous API call into a series of synchronous actions.
+ */
+export interface Middleware {
+  <S>(api: MiddlewareAPI<S>): (next: Dispatch) => (action: any) => any;
+}
+
+/**
+ * Creates a store enhancer that applies middleware to the dispatch method
+ * of the Redux store. This is handy for a variety of tasks, such as
+ * expressing asynchronous actions in a concise manner, or logging every
+ * action payload.
+ *
+ * See `redux-thunk` package as an example of the Redux middleware.
+ *
+ * Because middleware is potentially asynchronous, this should be the first
+ * store enhancer in the composition chain.
+ *
+ * Note that each middleware will be given the `dispatch` and `getState`
+ * functions as named arguments.
+ *
+ * @param middlewares The middleware chain to be applied.
+ * @returns A store enhancer applying the middleware.
+ */
+export function applyMiddleware(...middlewares: Middleware[]): StoreEnhancer;
+
+
+/* action creators */
+
+/**
+ * An *action creator* is, quite simply, a function that creates an action. Do
+ * not confuse the two terms—again, an action is a payload of information, and
+ * an action creator is a factory that creates an action.
+ *
+ * Calling an action creator only produces an action, but does not dispatch
+ * it. You need to call the store’s `dispatch` function to actually cause the
+ * mutation. Sometimes we say *bound action creators* to mean functions that
+ * call an action creator and immediately dispatch its result to a specific
+ * store instance.
+ *
+ * If an action creator needs to read the current state, perform an API call,
+ * or cause a side effect, like a routing transition, it should return an
+ * async action instead of an action.
+ *
+ * @template A Returned action type.
+ */
+export interface ActionCreator<A> {
+  (...args: any[]): A;
+}
+
+/**
+ * Object whose values are action creator functions.
+ */
+export interface ActionCreatorsMapObject {
+  [key: string]: ActionCreator<any>;
+}
+
+/**
+ * Turns an object whose values are action creators, into an object with the
+ * same keys, but with every function wrapped into a `dispatch` call so they
+ * may be invoked directly. This is just a convenience method, as you can call
+ * `store.dispatch(MyActionCreators.doSomething())` yourself just fine.
+ *
+ * For convenience, you can also pass a single function as the first argument,
+ * and get a function in return.
+ *
+ * @param actionCreator An object whose values are action creator functions.
+ *   One handy way to obtain it is to use ES6 `import * as` syntax. You may
+ *   also pass a single function.
+ *
+ * @param dispatch The `dispatch` function available on your Redux store.
+ *
+ * @returns The object mimicking the original object, but with every action
+ *   creator wrapped into the `dispatch` call. If you passed a function as
+ *   `actionCreator`, the return value will also be a single function.
+ */
+export function bindActionCreators<A extends ActionCreator<any>>(actionCreator: A, dispatch: Dispatch): A;
+
+export function bindActionCreators<
+  A extends ActionCreator<any>,
+  B extends ActionCreator<any>
+  >(actionCreator: A, dispatch: Dispatch): B;
+
+export function bindActionCreators<M extends ActionCreatorsMapObject>(actionCreators: M, dispatch: Dispatch): M;
+
+export function bindActionCreators<
+  M extends ActionCreatorsMapObject,
+  N extends ActionCreatorsMapObject
+  >(actionCreators: M, dispatch: Dispatch): N;
+
+
+/* compose */
+
+/**
+ * Composes single-argument functions from right to left. The rightmost
+ * function can take multiple arguments as it provides the signature for the
+ * resulting composite function.
+ *
+ * @param funcs The functions to compose.
+ * @returns R function obtained by composing the argument functions from right
+ *   to left. For example, `compose(f, g, h)` is identical to doing
+ *   `(...args) => f(g(h(...args)))`.
+ */
+export function compose(): <R>(a: R, ...args: any[]) => R;
+
+export function compose<A, R>(
+  f1: (b: A) => R,
+  f2: (...args: any[]) => A
+): (...args: any[]) => R;
+
+export function compose<A, B, R>(
+  f1: (b: B) => R,
+  f2: (a: A) => B,
+  f3: (...args: any[]) => A
+): (...args: any[]) => R;
+
+export function compose<A, B, C, R>(
+  f1: (b: C) => R,
+  f2: (a: B) => C,
+  f3: (a: A) => B,
+  f4: (...args: any[]) => A
+): (...args: any[]) => R;
+
+export function compose<R>(
+  f1: (a: any) => R,
+  ...funcs: Function[]
+): (...args: any[]) => R;