next() is not a function error Node.js

Question

var express = require('express');
var app = express();

var middleware = {
    requireAuthentication: function(req, res, next){
        console.log("private route hit");
        next();
    }
};

app.use(middleware.requireAuthentication());


app.get('/about',

    function(req, res){
    res.send('You clicked on about!');

    }

);  
var projectDir = __dirname + '/public'; 
app.use(express.static(projectDir));
app.listen(3000), function(){
    console.log('Static service started');

};

I get the error (when trying to run the server) that next() is not a function. I've been following a tutorial on Nodejs and it works just fine for them. What is the issue I am having here?

Answer 1

This line:

app.use(middleware.requireAuthentication());

calls your method and passes its return value into app.use. You're not calling it with any arguments, so naturally the next parameter is undefined.

Get rid of the () so you're passing the function, not its result, into app.use:

app.use(middleware.requireAuthentication);
// No () here --------------------------^