Store

A store is not a class. It's just an object with a few methods on it.To create it, pass your root to .

• dispatch(action)
• replaceReducer(nextReducer)

Returns the current state tree of your application.It is equal to the last value returned by the store's reducer.

Returns

(any): The current state tree of your application.

Dispatches an action. This is the only way to trigger a state change.

The store's reducing function will be called with the current getState() result and the given action synchronously. Its return value will be considered the next state. It will be returned from from now on, and the change listeners will immediately be notified.

Arguments

• action (Object†): A plain object describing the change that makes sense for your application. Actions are the only way to get data into the store, so any data, whether from the 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 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 could be constructed.

Returns

(Object^†): The dispatched action (see notes).

Notes

^† The “vanilla” store implementation you get by calling only supports plain object actions and hands them immediately to the reducer.

However, if you wrap createStore with , the middleware can interpret actions differently, and provide support for dispatching async actions. Async actions are usually asynchronous primitives like Promises, Observables, or thunks.

Middleware is created by the community and does not ship with Redux by default. You need to explicitly install packages like or redux-promise to use it. You may also create your own middleware.

To learn how to describe asynchronous API calls, read the current state inside action creators, perform side effects, or chain them to execute in a sequence, see the examples for .

Example

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 to read the current state tree inside the callback.

You may call from a change listener, with the following caveats:

• The subscriptions are snapshotted just before every 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 call, whether nested or not, will use a more recent snapshot of the subscription list.

• The listener should not expect to see all state 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 started will be called with the latest state by the time it exits.

It is a low-level API. Most likely, instead of using it directly, you'll use React (or other) bindings. If you commonly use the callback as a hook to react to state changes, you might want to write a custom observeStore utility. The Store is also an , so you can subscribe to changes with libraries like RxJS.

To unsubscribe the change listener, invoke the function returned by subscribe.

Arguments

• listener (Function): The callback to be invoked any time an action has been dispatched, and the state tree might have changed. You may call getState() inside this callback to read the current state tree. It is reasonable to expect that the store's reducer is a pure function, so you may compare references to some deep path in the state tree to learn whether its value has changed.

Returns

(Function): A function that unsubscribes the change listener.

Example

function select(state) {
  return state.some.deep.property
}
let currentValue
  let previousValue = currentValue
  currentValue = select(store.getState())
  if (previousValue !== currentValue) {
    console.log(
      'Some deep nested property changed from',
      previousValue,
      'to',
      currentValue
    )
  }
}
const unsubscribe = store.subscribe(handleChange)

Replaces the reducer currently used by the store to calculate the state.

It is an advanced API. 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.

Arguments

• nextReducer (Function) The next reducer for the store to use.