How to write production ready Node.js Rest API With javascript

index.js

var express = require("express"),
    bodyParser = require("body-parser"),
    app = express(),
    port = 3070;

// array to hold users
const users = [{firstName:"fnam1",lastName:"lnam1",userName:"username1"}];

app.use(bodyParser.json());

// Default user
app.get("/", function(req, res) {
    res.send("App works!!");
})

// request to get all the users
app.get("/users", function(req, res) {
    res.json(users);
})

// request to get all the users by userName
app.get("/users/:userName", function(req, res) {
    let user = users.filter(function(user){
        if(req.params.userName === user.userName){
            return user;
        }
    })
    res.json(user);
})

// request to post the user
// req.body has object of type {firstName:"fnam1",lastName:"lnam1",userName:"username1"}
app.post("/user", function(req, res) {
    users.push(req.body);
    res.json(users);
})

app.listen(port, function(err) {
    console.log("running server on from port:::::::" + port);
});

package.json

{
  "name": "user_api",
  "version": "1.0.0",
  "description": "sample rest api",
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Bhargav Bachina",
  "license": "ISC",
  "dependencies": {
    "body-parser": "^1.18.3",
    "express": "^4.16.4"
  }
}