issue deploying node.js server to heroku - node.js

Question

I am running into the error
An error occurred in the application and your page could not be served.
when running 'heroku open' command. On heroku dashboard it says deployed successfully but then it will not run 'it is working' from the app.get line of code.
server.js
const express = require('express');
const bodyParser = require('body-parser');
const bcrypt = require('bcrypt-nodejs');
const cors = require('cors');
const knex = require('knex');
const register = require('./controllers/register');
const signin = require('./controllers/signin');
const profile = require('./controllers/profile');
const image = require('./controllers/image');
const db = knex({
client: 'pg',
connection: {
host : '127.0.0.1',
user : 'benjohnson',
password : '',
database : 'smart-brain'
}
});
const app = express();
app.use(cors());
app.use(bodyParser.json());
app.get('/', (req, res)=> { res.send('its working!') })
app.post('/signin', signin.handleSignin(db, bcrypt))
app.post('/register', (req, res) => { register.handleRegister(req, res, db, bcrypt) })
app.get('/profile/:id', (req, res) => { profile.handleProfileGet(req, res, db)})
app.put('/image', (req, res) => { image.handleImage(req, res, db)})
app.post('/imageurl', (req, res) => { image.handleApiCall(req, res)})
app.listen(process.env.PORT || 3000, ()=> {
console.log(`app is running on port ${process.env.PORT}`);
})
When running the server.js file within the heroku cli i receive the error, when running 'heroku logs --tail' i receive this error?
> node#1.0.0 start /Users/benjohnson/.Trash
> nodemon server.js
sh: nodemon: command not found
npm ERR! file sh
npm ERR! code ELIFECYCLE
npm ERR! errno ENOENT
npm ERR! syscall spawn
npm ERR! node#1.0.0 start: `nodemon server.js`
npm ERR! spawn ENOENT
npm ERR!
npm ERR! Failed at the node#1.0.0 start script.
npm ERR! This is probably not a problem with npm. There is likel
y additional logging output above.
npm WARN Local package.json exists, but node_modules missing, di
d you mean to install?
npm ERR! A complete log of this run can be found in:
npm ERR! /Users/benjohnson/.npm/_logs/2019-09-25T14_11_11_91
0Z-debug.log

Answer 1

The error is about nodemon.
Open the package.json, is at the same folder with server.js
Find:
"scripts": {
"start": " nodemon server.js",
},
And replace it with:
"scripts": {
"start": "node server.js",
"start:dev": "nodemon server.js"
},
Upload again in Heroku.
When you want to run the project locally, just run in your terminal npm start:dev and it will load server.js with nodemon.