I want to preserve backend data on reload - node.js

Question

I have created an app that has a cart that sends data to the backend, now when I restore I want to preserve the data and display the same data as before.
I have used the PUT method instead of POST and when I send and get data from Firebase, data is preserved on reload and the data from the database is visible, but if I use my own backend in Node.js, I am not able to get the data on reload. This is where I am fetching data from the backend.
export const fetchCartData=()=>{
return async(dispatch)=>{
const getData= async() =>{
const response = await fetch('https://localhost:5000/');
if(!response.ok){
throw new Error('Something went wrong');
}
const info=await response.json();
return info;
};
try{
const data= await getData();
console.log("Here is data from Firebase", data);
dispatch(order_action.replaceCart({
items:data.items || [],
totalQuantity:data.totalQuantity || 0
}));
}catch(error){
dispatch(show_action.showNotification({
status:"failed",
title:"Error...",
message:"Some error occurred."
}));
}
}
}
Tha backend Code is:
const express=require("express");
const bodyParser=require('body-parser');
const cors=require('cors');
const app=express();
app.use(cors());
app.use(bodyParser.json());
app.put("/",function (req,res) {
const data={
items:req.body.items,
totalQuantity:req.body.totalQuantity
}
console.log(data);
console.log("END");
res.send({data});
})
app.get("/",function (req,res) {
console.log(req.body);
const data={
items:req.body.items,
totalQuantity:req.body.totalQuantity
}
res.send({data})
})
app.listen(5000,function () {
console.log("Running on 5000");
})

Answer 1

You can use localStorage on the browser i.e at the client-side. Whenever there is any change in the cart do these steps:
Send data to the backend API using the PUT method and store it in DB or cache(based on the website and users you are dealing with).
Once you get the response from API, update your localStorage data.
localStorage.set('cart', JSON.stringify(dataFromAPI));
Now, on every reload you will always be getting the last updated cart data.
when I send and get data from Firebase, data is preserved on reload
and the data from the database is visible
Just for your knowledge, firebase is a database and when you save data, it is persistent. Now, on reload you must be calling the firebase DB to get the data back that's why you see the data on the client otherwise it is impossible to get data without caching or saving it locally.

Answer 2

You can store/contain the data in a JSON file and reuse the data.
If the data is a stream of data, then you do only need some latest records; you can perform some JavaScript array operations to perform a First-In-First-Out operations by containing up to like 50 or 100 objects/records in the JSON file, so you can later retrieve/reuse.
const fs = require("fs");
const path = require("path");
const data = fs.readFileSync(path.resolve(__dirname,"filename.json");
const data = JSON.parse(data);
data.contentArray.push(req.body); //or any other data
const data = JSON.stringify(data);
fs.writeFileSync(path.resolve(__dirname,"filename.json",data,"utf-8");
/*
filename.json sample
{
"contentArray":[
{
"key":"value"
},
{
"key":"value"
}
]
}
*/
You can find ways to literally store/contain the data in a '.json' file or '.csv' file. I would recommend storing the data in a JSON file, which is way easier.