Implement Nodejs with pm2 start in Docker - node.js

Question

I have a nodejs app. The app runs with pm2. When I execute "pm2 start app.js". pm2 is started. But when I do curl http://localhost:3000 , it says : Failed to connect to localhost port 3000: Connection refused. But port 3000 is open. I am confused, Please help me out.
My Dockerfile
FROM keymetrics/pm2:latest-alpine
# Create app directory
RUN mkdir -p /usr/cl/app
WORKDIR /usr/cl/app
# Install app dependencies
COPY package*.json ./
COPY . .
RUN npm install
RUN npm install pm2 -g
EXPOSE 3000
CMD [ "npm", "start" ]
My Package.json
{
"name": "cs",
"version": "1.0.0",
"description": "Cs",
"main": "app.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1",
"start": "pm2 start app.js"
},
"author": "",
"license": "ISC",
"dependencies": {
"async": "^2.6.0",
"axios": "^0.18.0",
"base64-encode-decode": "0.0.3",
"body-parser": "^1.18.3",
"cors": "^2.8.4",
"csv": "^1.2.1",
"csv2sql-lite": "0.0.6",
"dotenv": "^4.0.0",
"epipebomb": "^1.0.0",
"express": "^4.16.3",
"fast-csv": "^2.4.1",
"getmac": "^1.4.1",
"ini": "^1.3.5",
"js-md5": "^0.7.3",
"multer": "^1.3.0",
"node-cache": "^4.2.0",
"node-xlsx": "^0.12.0",
"nodemailer": "^4.6.4",
"os": "^0.1.1",
"pg": "^6.4.2",
"serve-static": "^1.13.2",
"trim": "0.0.1"
}
}
Docker image and container is created. But when I do curl http://localhost:3000
Error says "Failed to connect to localhost port 3000: Connection refused. But port 3000 is open. I am confused, Please help me out.
app.js file is
"var express = require('express');
var bodyparser = require('body-parser');
var cors = require('cors');
var path = require('path');
require('dotenv').config({path: 'inireader.env'});
var app = express();
const port = 3000;
const routepostgres = require('./routes/routepostgres');
app.use(cors());
app.use(bodyparser.urlencoded({ extended: false }));
app.use(bodyparser.json());
app.use(express.static(path.join(__dirname,'public')))
app.use('/api', routepostgres);
app.listen(port, function(req, res){
console.log('Server started at port:'+ port);
});
app.get('/', function(req, res){
res.send('Welcome # browser');
console.log('Welcome # Console');
});