app.js

const express = require('express');
const morgan = require('morgan');
const body = require('body-parser');
const app = express();
const mongoose = require('mongoose');
const productRoutes = require('./api/routes/products');
const orderRoutes = require('./api/routes/orders');

const connection = mongoose.connect(
    'mongodb://' + process.env.MONG_UN + ':' + process.env.MONG_PW + 
    '@node-api-shard-00-00-8epfm.mongodb.net:27017, \
    node-api-shard-00-01-8epfm.mongodb.net:27017, \
    node-api-shard-00-02-8epfm.mongodb.net:27017/test?ssl=true&replicaSet=node-api-shard-0&authSource=admin&retryWrites=true&w=majority',
    {
        useNewUrlParser: true,
        // useUnifiedTopology: true
    }
)
// connection.then(res => {
//     console.log('Connected');
// });
// connection.catch(err => {
//     console.log('error zahid '+ err)
// });
mongoose.connection.on('connected', () => console.log('Connected'));
mongoose.connection.on('error', (err) => console.log('Connection failed with - ',err));
app.use(morgan('dev'));
app.use(body.urlencoded({ extended: false }));
app.use(body.json({}));

app.use((req, res, next) => {
    res.header('Access-Control-Allow-Origin', '*');
    res.header('Access-Control-Allow-Headers',
    'Origin, X-Requested-With, Content-Type, Accept, Authorization'
    );
    if (req.method === 'OPTIONS') {
        res.header('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, PATCH');
        return res.status(200).json({});
    }
    next();
});
//routes which will handle incoming requests
app.use('/products', productRoutes);

app.use('/orders', orderRoutes);

app.use(function(req, res, next) {
    const error = new Error('Not found');
    error.status = 404;
    next(error);
});

app.use((error, req, res, next) => {
    res.status(error.status || 500);
    res.json({
        error: {
            message: error.message
        }
    });
});

module.exports= app;