*npm init
*npm install express 
*npm install nodemon
*npm install body-parser
*npm install mongodb --save
**********************************
	connection mongodb---
**********************************
	const MongoClient = require('mongodb').MongoClient;
// 
require('dotenv').config();
const url = process.env.DB_URL;
MongoClient.connect(url, {
    useUnifiedTopology: true
}, (err, db) => {
    if (err) throw err;

    const dbo = db.db(process.env.DB_NAME);
    dbo.listCollections().toArray(function(err, items) {
        if (err) throw err;

        if (items.length == 0) {
            dbo.createCollection("category_img", (err, res) => {
                if (err) onsole.log("error", err);
                db.close();
            });
            dbo.createCollection("category_type", (err, res) => {
                if (err) console.log("error", err);
                db.close();
            });
            dbo.createCollection("user_logs", (err, res) => {
                if (err) console.log("error", err);
                db.close();
            });
            console.log("collections created")
        }

    });
    console.log("connection created")

});

module.exports = MongoClient

**********************
	cors
**********************
*npm instal cors

	const cors = require('cors');
	
	app.use(cors({ origin: true, credentials: true }))
app.use(function(req, res, next) {

    res.header("Access-Control-Allow-Origin", req.headers.origin);
    res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS, PUT, PATCH, DELETE');
    res.setHeader('Access-Control-Allow-Headers', 'X-Requested-With,content-type');
    res.setHeader('Access-Control-Allow-Credentials', true);
    next();
});