TypeError: app.listen is not a function NODEJS

I cant understand why I see this error.

my app.js file

const express = require("express");
const morgan = require('morgan');
const app = express();

const tourRouter = require('./routers/tourRouter');
const userRouter = require('./routers/userRouter');

app.use(express.json());
app.use(morgan('dev'));
app.use((req,res,next)=>{
    req.RequestTime = new Date().toISOString();
    next();
});

app.use('/api/v1/tours',tourRouter);
app.use('/api/v1/users',userRouter);
const port = 3000;
app.listen(port, () => {
    console.log(`App running on port ${port}`);
});

this runs without a problem, but when I cut

const port = 3000;
app.listen(port, () => {
    console.log(`App running on port ${port}`);
});

this part and I write app.js folder exports.module = app; and I create server.js file

const app = require('./app');
const port = 3000;
app.listen(port, () => {
    console.log(`App running on port ${port}`);
});

this doesn't work and I get

TypeError: app.listen is not a function

As @Dickens A S commented, you need to assign the object: app: instance of express to the module.exports in the file: "app.js".

Read Doc: Node.js: module.exports

many want their module to be an instance of some class. To do this, assign the desired export object to module.exports.

Add this in the of of file:app.js:

module.exports = app;