TypeError: Class constructor MongoStore cannot be invoked without 'new'

 This error occurs as because may be you have used the following code: 

const MongoStore= require('connect-mongo')(session);

and

app.use(session({

    secret: 'keyboard cat',

    resave: false,

    saveUninitialized: false,

    store: new MongoStore({ mongooseConnection: mongoose.connection })

}));

Now this is happening as because syntax have been changed (see the documentation here: documentation)

Solution that worked for me: 

Use this: 

const MongoStore= require('connect-mongo');

and, 

app.use(session({

    secret: 'keyboard cat',

    resave: false,

    saveUninitialized: false, //false means don't create a session untitl it is stored

    // store: new MongoStore({ mongooseConnection: mongoose.connection })

    store: MongoStore.create({

        mongoUrl: process.env.MONGO_URI

    })

}));