Unexpected end of JSON Input while parsing json file read asynchronously

Question

I am new to node js and using MVC pattern in my project so when I am trying to add products to my cart.json file I am facing the issue

routes file

const Product = require('../models/product');
const Cart = require('../models/cart')

exports.postcart = (req,res,next) => {
    const proid = req.params.productcartid
    Product.findbyid(proid).then(function(value) {
        console.log(value.price)    // prints the price correctly so the producted is received as an argument
        Cart.addProduct(proid, value.price)
    })
}

Product model

  module.exports = class Product {
      // constructor function here 

      save() {
          //saving the products here, works fine
      }

      static findbyid(id) {
          const p = path.join(path.dirname(process.mainModule.filename), 'data', 'products.json') 
          return new Promise((resolve, reject) => {
               fs.readFile(p, (err, data) => {
                   const allproducts = JSON.parse(data)
                   const result = allproducts.find(p => p.id === id)
                   return resolve(result)   
               })
          })
      } 
  }

Cart model

module.exports = class Cart {
static addProduct(id, price) {
    const p=path.join(path.dirname(process.mainModule.filename),
'data','cart.json')
    fs.readFile(p, (error, file) => {
        console.log('sgdf',id);
        let cart = {
            products: [],
            totalPrice: 0
        };
        if(!error) {
            console.log('inside error') //prints in console
            cart = JSON.parse(file);
        }
        console.log('outside error') //does not output this and anything below from here too doesn't prints in the console

        const existingProductIndex = cart.products.findIndex(p => 
p.id === id);
        console.log('dghjhjghfg',existingProductIndex) ////does not output this 
        const existingProduct = 
cart.products[existingProductIndex];
        if(existingProduct) {
            existingProduct.qty += 1;
        }
        else {
            cart.products.push({
                id,
                qty: 1
            });
        }
        cart.totalPrice += Number(price);
        console.log(cart);
        fs.writeFile(p, JSON.stringify(cart), error => {
            if(error) return console.error(error);
        });
    });
}

};

cart.js

const fs=require('fs')
const path=require('path')
module.exports = class Cart {

static addProduct(id, price) {
    const 
 p=path.join(path.dirname(process.mainModule.filename),
'data','cart.json')
    fs.readFile(p, (error, file) => {
        console.log('sgdf',id);
        let cart = {
            products: [],
            totalPrice: 0
        };
        if(!error) {
            console.log('insdie error')
            console.log(file)
            cart = JSON.parse(file)
        }
        console.log('outside error')

        const existingProductIndex = cart.products.findIndex(p => p.id 
  === id);
        console.log('dghjhjghfg',existingProductIndex)
        const existingProduct = cart.products[existingProductIndex];
        if(existingProduct) {
            existingProduct.qty += 1;
        }
        else {
            cart.products.push({
                id,
                qty: 1
            });
        }
        console.log('adsgfdgfh')
        cart.totalPrice += Number(price);
        console.log(cart);
        fs.writeFile(p, JSON.stringify(cart), error => {
            if(error) return console.error(error);
        });
    });
    }
   };

The error i am facing is

undefined:1



SyntaxError: Unexpected end of JSON input
at JSON.parse (<anonymous>)
at /Users/ratnabhkumarrai/Desktop/max-project/models/cart.js:15:29
at FSReqCallback.readFileAfterClose [as oncomplete] 
(internal/fs/read_file_context.js:61:3)

In my Cart models when i try to console log and see i find that only my half of the code is executed the console log that i tried below does not get executed....What am i doing wrong here ?

Answer 1

I got this fixed by using writeFileSync instead of writeFile. I was trying to read a file that hadn't been closed yet