“void”类型的参数不可分配给“PathParams”类型的参数

Question

Created route handler and while adding in my route .

import {Application, NextFunction} from 'express';
import {container} from 'tsyringe';
const routeConstantsArray  = { };

const constants: any  = []
constants.push(routeConstantsArray)
let next : NextFunction;
export const loadConstantsMiddleware = (app:Application) => {
    app.locals = constants
    next();
};

Route

import express from 'express';
import {Application} from 'express';
import cors from 'cors';
// Import Internal Modules
import {loadConstantsMiddleware} from '../core/middleware/constants_middleware';
 const startupRouterConfig = (app: Application): Application => {
    app.use(cors());
    app.use(express.json());
    app.use(loadConstantsMiddleware(app));
    return app;
};

Error
(parameter) app: express.Application No overload matches this call. The last overload gave the following error:

Argument of type 'void' is not assignable to parameter of type 'PathParams'.ts(2769)
index.d.ts(55, 5): The last overload is declared here.

Answer 1

To use the loadConstantsMiddleware as middleware, you have to return a request handler, like:

export const loadConstantsMiddleware = (app:Application) => {
    app.locals = constants;
    return (req, res, next) => {
      next();
    }
};

But in this scenario, it probably doesn't make sense to use it as a middleware since the constants are scoped to the entire application (versus just the request).

To just add it to the app directly, without middleware, you can do:

// main
app.use(cors());
app.use(express.json());
loadConstantsMiddleware(app);

// load-constants-middleware
export const loadConstantsMiddleware = (app:Application) => {
  app.locals = constants
};