How to store data in database.db w/o data-loss?

Question

I'm trying to save multiple data from different files into database.db without any libraries such as MongoDB or MySQL.

A problem is database.db keeps overwriting when it receives new data from each instance.

{"score":12} // It only saves the last data.

Furthermore, when I refresh the browser constantly, sometimes the data is going to merge in a weird pattern like this:

{"score":12}p"} // That p is the last letter of a word from first instance, 'Temp'.

This is how I've done in the code:

// instance1.js
class A {
    constructor(name) {
        this.name = name
        this.post();
    }
    async post() {
        const options = {
            method: 'POST',
            headers: {
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(this)
        };
        const response = await fetch('/', options);
        const json = await response.json();
    }
}
let newa = new A('Temp');

// instance2.js
class B {
    constructor(score) {
        this.score = score
        this.post();
    }
    async post() {
        const options = {
            method: 'POST',
            headers: {
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(this)
        };
        const response = await fetch('/', options);
        const json = await response.json();
        }
}
let newb = new B(12);

// server.js
const express = require('express');
const fs = require('fs');
const app = express();

app.listen(3000, () => console.log('initialized . . .'));
app.use(express.static('public'));
app.use(express.json({limit: '10mb'}));

app.post('/', (request, response) => {
    var instance = request.body,
        object = JSON.stringify(instance);
    fs.writeFile('database.db', object, () => {
        console.log(object);
    });
    response.json(request.body);
})

My goal is to save objects into the database for sending back to the client-side javascript.

Are there any ways to store the data w/o overwriting and how to prevent unwanted merging?

Answer 1

I my opinion you should change in post request writeFile to appendFile

app.post('/', (request, response) => {
  var object = JSON.stringify(request.body);
  fs.appendFile('database.db', object, (data) => {
    console.log(data);
  });
  response.json(request.body);
})