redux: Error in types for middleware (typescript 2.4.1)

It is a bug

I have this simple middleware:

import { Middleware, Store, Dispatch, Action } from 'redux';
import { AppState } from 'types/appState';

export default function createSimpleMiddleware(): Middleware {
  return (store: Store<AppState>) => (next: Dispatch<AppState>) => (action: Action): Action => {
    return next(action);
  };
}

It is useless, but there is a problem) This code works with typescript version 2.3.x and below. But in typescript 2.4 there is an Error.

What is the current behavior? In typescript I have this Error:

Types of parameters 'store' and 'api' are incompatible.
    Type 'MiddlewareAPI<S>' is not assignable to type 'Store<AppState>'.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://jsfiddle.net or similar.

You can find demo code at the top of current issue.

What is the expected behavior?

I expect, that there won’t be any errors.

Which versions of Redux, and which browser and OS are affected by this issue? Did this work in previous versions of Redux?

Typescript: 2.4.1 Redux: 3.7.1 NodeJS: 6.9.1 OS: MacOS

About this issue

Original URL
State: closed
Created 7 years ago
Comments: 19 (4 by maintainers)

Commits related to this issue

Merge pull request #2481 from reduxjs/fix-2477 — committed to brandoncroberts/redux by markerikson 2 years ago

Most upvoted comments

This is my workaround for now:

declare module 'redux' {
  export interface Middleware<T=any> {
    <S>(api: MiddlewareAPI<S>): (next: Dispatch<S>) => Dispatch<S>;
    (api: MiddlewareAPI<T>): (next: Dispatch<T>) => Dispatch<T>;
  }
}

@timdorr Shouldn’t we reopen this until it is fixed?

tbo on Jul 24, 2017

@artem-malko after typescript@2.4.x change the generics check,

Middleware should change the position ofS too.

export interface Middleware<S> {
  (api: MiddlewareAPI<S>): (next: Dispatch<S>) => Dispatch<S>;
}

morlay on Jul 6, 2017

Please reopen, this is not fixed yet. I still have the same error too

TypeScript: 2.4.2 Redux: 3.7.2 NodeJS: 7.7.3 OS: MacOS

davidka on Jul 26, 2017

@macdonaldr93 See the tests for Middleware types.

aikoven on Feb 19, 2018

Is it possible to add an example of what a valid middleware would look like with typescript? Even after following this thread, I’m unsure how to update my middleware so that it compiles correctly and types are satisfied.

macdonaldr93 on Feb 17, 2018