无法在Heroku上运行我的第一个MEAN应用程序

server.js file:

var port = Number(process.env.PORT || 3000);
var express = require('express');
var app = require('./app');
var debug = require('debug')('myapp:server');
var http = require('http');
app.set('port', port);
var server = http.createServer(app);
server.listen(port);
var port = Number(process.env