Fixing the "Cannot invoke an expression without a call signature" typescript error in Visual Studio using the C# React/Redux template

Upon creating a new project using the C# React/Redux Web Application template in Visual Studio, an error is detected within the "\ClientApp\configureStore.ts" file.

The specific issue highlights that "createStoreWithMiddleware(allReducers, initialState)" is marked with a red underline and the error message reads:

"TS2349 (TS) Cannot invoke an expression whose type lacks a call signature. Type '{}' has no compatible call signatures."

STEPS TO REPRODUCE THE ERROR:

  • Launch VS 2017 Community Edition version 15.3.4
  • Create a fresh C# web project utilizing .NET framework 4.7
  • Select the React/Redux Web Application template along with .NET Core version 2.0
  • After loading the project, there might be missing npm dependencies which can be resolved by opening the project folder in the Package Manager console and executing "npm install npm@latest -g"
  • Following this fix, the site loads properly but the mentioned error related to "createStoreWithMiddleware(allReducers, initialState)" persists.

Simply ignoring or suppressing the error doesn't seem like the best approach, considering it might be as straightforward as defining a call signature or downcasting. Given my limited knowledge in TypeScript, I seek guidance for this seemingly basic question.

[UPDATE] - Removing the following line of code resolves the error display. However, disabling this line affects the functionality of devTools extension, prompting the need to understand its purpose in order to resolve the error without compromising essential features:

devToolsExtension ? devToolsExtension() : <S>(next: StoreEnhancerStoreCreator<S>) => next

Below is the content of the "configureStore.ts" file - any assistance provided in advance would be greatly appreciated!

import { createStore, applyMiddleware, compose, combineReducers, GenericStoreEnhancer, Store, StoreEnhancerStoreCreator, ReducersMapObject } from 'redux';
import thunk from 'redux-thunk';
import { routerReducer, routerMiddleware } from 'react-router-redux';
import * as StoreModule from './store';
import { ApplicationState, reducers } from './store';
import { History } from 'history';

export default function configureStore(history: History, initialState?: ApplicationState) {
    // Middleware construction to process actions before they reach the store.
    const windowIfDefined = typeof window === 'undefined' ? null : window as any;
    
    const devToolsExtension = windowIfDefined && windowIfDefined.devToolsExtension as () => GenericStoreEnhancer;
  
    const createStoreWithMiddleware = compose(
        applyMiddleware(thunk, routerMiddleware(history)),
        devToolsExtension ? devToolsExtension() : <S>(next: StoreEnhancerStoreCreator<S>) => next
    )(createStore);

    // Combining all reducers and initializing the app-wide store instance.
    const allReducers = buildRootReducer(reducers);
    const store = createStoreWithMiddleware(allReducers, initialState) as Store<ApplicationState>;

    // Support for hot module replacement for reducers via Webpack
    if (module.hot) {
        module.hot.accept('./store', () => {
            const nextRootReducer = require<typeof StoreModule>('./store');
            store.replaceReducer(buildRootReducer(nextRootReducer.reducers));
        });
    }

    return store;
}

function buildRootReducer(allReducers: ReducersMapObject) {
    return combineReducers<ApplicationState>(Object.assign({}, allReducers, { routing: routerReducer }));
}

Answer №1

The reason behind this issue is that the non-generic compose() function generates a function without any specified parameters. To rectify this error, it is recommended to explicitly utilize the generic compose<T>() function which returns the fundamental type of

StoreEnhancerStoreCreator<any>
. This specific type does indeed accept the two parameters you are attempting to pass, thereby enabling full intellisense when invoking createStoreWithMiddleware:

const createStoreWithMiddleware = compose<StoreEnhancerStoreCreator<any>>(
    applyMiddleware(thunk, routerMiddleware(history)),
    devToolsExtension ? devToolsExtension() : <S>(next: StoreEnhancerStoreCreator<S>) => next
)(createStore);

// remains unchanged:
const store = createStoreWithMiddleware(allReducers, initialState) as Store<ApplicationState>;

It is advisable to refrain from casting something as <any> (reminiscent of C#'s object type) unless absolutely necessary. Such casting undermines TypeScript's type checking functionality, a principal aspect of utilizing TypeScript. For instance, if a function can exclusively return Cat, Dog, or Human, designate it as Mammal. Subsequently, if you introduce Snakes, you can define them under the umbrella of Animal.

Answer №2

Regrettably, the origins of the SPA project templates remain unknown to me, making it impossible for me to verify if this particular issue is already being addressed or resolved.

Nevertheless, you have the power to rectify this issue within your local project on your own accord. The main problem lies in the fact that the compose function fails to return a properly typed callable, resulting in the prohibition of calling createStoreWithMiddleware. You can remedy this by adjusting the type information in various ways. One viable solution involves modifying the line where the error surfaces as follows:

const store = (<any>createStoreWithMiddleware)(allReducers, initialState) as Store<ApplicationState>;

This action essentially casts createStoreWithMiddleware to the any type, signaling TypeScript to treat it as unidentified and accept any form of input. Additionally, since the function call's outcome is explicitly labeled using as Store<ApplicationState>, complications are unlikely to arise in subsequent stages of development.

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