index.js

const express = require('express');
const paypal = require('paypal-rest-sdk');
const fs=require('fs');
const exphdbs=require('express-handlebars');
var path=require('path');
const app = express();


app.set('views',path.join(__dirname,"views"));
app.engine('handlebars',exphdbs({defaultLayout:'main'}));
app.set('view engine','handlebars');

paypal.configure({
  'mode': 'sandbox', //sandbox or live
  'client_id': 'AXMeJ1HaMiTJqoZAXDezOC_NQtXZjYGH55WmJVTvqtrZgkva2xN1NkPQzR8eFyrUWR6TiK9y3YzWLpws',
  'client_secret': 'EDtLfGhK53kOEEbVhTb0kzwcLCwfmRBsgYzTvJ9q3HZ9SgWXL6fGlMWs33hCbKe7RQENxXkGpabYDmok'
});


var items=JSON.parse(fs.readFileSync('items.json'));
var total =0;
for(i = 0;i<items.length;i++)
{
  total+=parseFloat(items[i].price)*items[i].quantity;
}

app.get('/', function(req, res){
  res.render('index');
});

app.post('/pay',function(req,res){
  const create_payment_json = {
    "intent": "sale",
    "payer": {
        "payment_method": "paypal"
    },
    "redirect_urls": {
        "return_url": "http://localhost:3000/success",
        "cancel_url": "http://localhost:3000/cancel"
    },
    "transactions": [{
        "item_list": {
            "items": items
        },
        "amount": {
            "currency": "USD",
            "total": total.toString()
        },
        "description": "Hat for the best team ever"
    }]
};

paypal.payment.create(create_payment_json, function (error, payment) {
  if (error) {
    res.render('cancle');
  } else {
      for(let i = 0;i < payment.links.length;i++){
        if(payment.links[i].rel === 'approval_url'){
          res.redirect(payment.links[i].href);
        }
      }
  }
});

});
app.get('/cancle', function(req, res){
  res.render('cancle');
});
app.get('/success', (req, res) => {
  const payerId = req.query.PayerID;
  const paymentId = req.query.paymentId;

  const execute_payment_json = {
    "payer_id": payerId,
    "transactions": [{
        "amount": {
            "currency": "USD",
            "total": total.toString()
        }
    }]
  };

  paypal.payment.execute(paymentId, execute_payment_json, function (error, payment) {
    if (error) {
       res.render('cancle');
    } else {
        console.log(JSON.stringify(payment));
        res.render('success');
    }
});
});

app.get('/cancel', (req, res) => res.send('Cancelled'));

app.listen(3000, function(){
  console.log(total);
});