Simple configurable Express middleware not executing - node.js

Question

I'm trying to build a configurable middleware (a custom middleware function that takes custom parameters, and returns a (req,res,next) function that uses these parameters) in Express. However, I can't get this middleware to execute on a router.get() call.
The expected behaviour in the code below is that, when trying to GET the home page (/), the console logs 'success!' then I get a 404 (as the next() in the middleware will pass me on to the 404 function).
However, nothing happens and the request times out. The function is being detected, as when I put the console.log() in the middleware but just before the return function(req,res,next){ line, I am seeing the output on the console. I only get this issue when the configurable middleware is returning a function.
./app.js (no changes to the template that Express builds):
var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');
var indexRouter = require('./routes/index');
var usersRouter = require('./routes/users');
var app = express();
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');
app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use('/', indexRouter);
app.use('/users', usersRouter);
// catch 404 and forward to error handler
app.use(function(req, res, next) {
next(createError(404));
});
// error handler
app.use(function(err, req, res, next) {
// set locals, only providing error in development
res.locals.message = err.message;
res.locals.error = req.app.get('env') === 'development' ? err : {};
// render the error page
res.status(err.status || 500);
res.render('error');
});
module.exports = app;
./routes/index.js:
var express = require('express');
var router = express.Router();
var simplemiddleware = require('../middlewares/simplemiddleware');
/* GET home page. */
router.get('/', function(req, res, next) {
simplemiddleware.simpleReturn('success!');
});
module.exports = router;
./middlewares/simplemiddleware.js:
exports.simpleReturn = function (outputString){
return function (req,res,next) {
console.log(outputString);
next();
}
}

Answer 1

Please note that the
var simplemiddleware = require('../middlewares/simplemiddleware');
actually is a function, to fix the problem, please try the following.
./routes/index.js:
var simplemiddleware = require('../middlewares/simplemiddleware');
/* GET home page. */
router.get('/', function(req, res, next) {
// note `simplemiddleware.simpleReturn(str)` returns a function
let func = simplemiddleware.simpleReturn('success!');
// run the middleware
func(req, res, next);
});