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getDefaultMiddleware

Returns an array containing the default list of middleware.

Intended Usage​

By default, configureStore adds some middleware to the Redux store setup automatically.

const store = configureStore({
  reducer: rootReducer,
})

// Store has middleware added, because the middleware list was not customized

If you want to customize the list of middleware, you can supply an array of middleware functions to configureStore:

const store = configureStore({
  reducer: rootReducer,
  middleware: [thunk, logger],
})

// Store specifically has the thunk and logger middleware applied

However, when you supply the middleware option, you are responsible for defining all the middleware you want added to the store. configureStore will not add any extra middleware beyond what you listed.

getDefaultMiddleware is useful if you want to add some custom middleware, but also still want to have the default middleware added as well:

import { configureStore } from '@reduxjs/toolkit'

import logger from 'redux-logger'

import rootReducer from './reducer'

const store = configureStore({
  reducer: rootReducer,
  middleware: (getDefaultMiddleware) => getDefaultMiddleware().concat(logger),
})

// Store has all of the default middleware added, _plus_ the logger middleware

It is preferable to use the chainable .concat(...) and .prepend(...) methods of the returned MiddlewareArray instead of the array spread operator, as the latter can lose valuable type information under some circumstances.

Included Default Middleware​

Development​

One of the goals of Redux Toolkit is to provide opinionated defaults and prevent common mistakes. As part of that, getDefaultMiddleware includes some middleware that are added in development builds of your app only to provide runtime checks for three common issues:

  • Immutability check middleware: deeply compares state values for mutations. It can detect mutations in reducers during a dispatch, and also mutations that occur between dispatches (such as in a component or a selector). When a mutation is detected, it will throw an error and indicate the key path for where the mutated value was detected in the state tree. (Forked from redux-immutable-state-invariant.)

  • Serializability check middleware: a custom middleware created specifically for use in Redux Toolkit. Similar in concept to immutable-state-invariant, but deeply checks your state tree and your actions for non-serializable values such as functions, Promises, Symbols, and other non-plain-JS-data values. When a non-serializable value is detected, a console error will be printed with the key path for where the non-serializable value was detected.

  • Action creator check middleware: another custom middleware created specifically for use in Redux Toolkit. Identifies when an action creator was mistakenly dispatched without being called, and warns to console with the action type.

In addition to these development tool middleware, it also adds redux-thunk by default, since thunks are the basic recommended side effects middleware for Redux.

Currently, the return value is:

const middleware = [
  actionCreatorInvariant,
  immutableStateInvariant,
  thunk,
  serializableStateInvariant,
]

Production​

Currently, the return value is:

const middleware = [thunk]

Customizing the Included Middleware​

getDefaultMiddleware accepts an options object that allows customizing each middleware in two ways:

  • Each middleware can be excluded the result array by passing false for its corresponding field
  • Each middleware can have its options customized by passing the matching options object for its corresponding field

This example shows excluding the serializable state check middleware, and passing a specific value for the thunk middleware's "extra argument":

import { configureStore } from '@reduxjs/toolkit'
import rootReducer from './reducer'
import { myCustomApiService } from './api'

const store = configureStore({
  reducer: rootReducer,
  middleware: (getDefaultMiddleware) =>
    getDefaultMiddleware({
      thunk: {
        extraArgument: myCustomApiService,
      },
      serializableCheck: false,
    }),
})

API Reference​

interface ThunkOptions<E = any> {
  extraArgument: E
}

interface ImmutableStateInvariantMiddlewareOptions {
  // See "Immutability Middleware" page for definition
}

interface SerializableStateInvariantMiddlewareOptions {
  // See "Serializability Middleware" page for definition
}

interface ActionCreatorInvariantMiddlewareOptions {
  // See "Action Creator Middleware" page for definition
}

interface GetDefaultMiddlewareOptions {
  thunk?: boolean | ThunkOptions
  immutableCheck?: boolean | ImmutableStateInvariantMiddlewareOptions
  serializableCheck?: boolean | SerializableStateInvariantMiddlewareOptions
  actionCreatorCheck?: boolean | ActionCreatorInvariantMiddlewareOptions
}

function getDefaultMiddleware<S = any>(
  options: GetDefaultMiddlewareOptions = {}
): Middleware<{}, S>[]
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