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Serializability Middleware#

A custom middleware that detects if any non-serializable values have been included in state or dispatched actions, modeled after redux-immutable-state-invariant. Any detected non-serializable values will be logged to the console.

This middleware is added to the store by default by configureStore and getDefaultMiddleware.

You can customize the behavior of this middleware by passing any of the supported options as the serializableCheck value for getDefaultMiddleware.


interface SerializableStateInvariantMiddlewareOptions {
* The function to check if a value is considered serializable. This
* function is applied recursively to every value contained in the
* state. Defaults to `isPlain()`.
isSerializable?: (value: any) => boolean
* The function that will be used to retrieve entries from each
* value. If unspecified, `Object.entries` will be used. Defaults
* to `undefined`.
getEntries?: (value: any) => [string, any][]
* An array of action types to ignore when checking for serializability.
* Defaults to []
ignoredActions?: string[]
* An array of dot-separated path strings to ignore when checking
* for serializability, Defaults to ['meta.arg']
ignoredActionPaths?: string[]
* An array of dot-separated path strings to ignore when checking
* for serializability, Defaults to []
ignoredPaths?: string[]
* Execution time warning threshold. If the middleware takes longer
* than `warnAfter` ms, a warning will be displayed in the console.
* Defaults to 32ms.
warnAfter?: number
* Opt out of checking state, but continue checking actions
ignoreState?: boolean



Creates an instance of the serializability check middleware, with the given options.

You will most likely not need to call this yourself, as getDefaultMiddleware already does so.


import { Iterable } from 'immutable'
import {
} from '@reduxjs/toolkit'
import reducer from './reducer'
// Augment middleware to consider Immutable.JS iterables serializable
const isSerializable = (value: any) =>
Iterable.isIterable(value) || isPlain(value)
const getEntries = (value: any) =>
Iterable.isIterable(value) ? value.entries() : Object.entries(value)
const serializableMiddleware = createSerializableStateInvariantMiddleware({
const store = configureStore({
middleware: [serializableMiddleware],


Checks whether the given value is considered a "plain value" or not.

Currently implemented as:

import isPlainObject from './isPlainObject'
export function isPlain(val: any) {
return (
typeof val === 'undefined' ||
val === null ||
typeof val === 'string' ||
typeof val === 'boolean' ||
typeof val === 'number' ||
Array.isArray(val) ||

This will accept all standard JS objects, arrays, and primitives, but return false for Dates, Maps, and other similar class instances.