append data to an existing Json file in nodejs - node.js

Question

i'm trying to add new data in an existing json file named db.json which i use to store data locally aka inMemory.So i tried many ways to achieve that but still not working as expected Since the add operation replaced the existing data.
For example i want something like this :
{
"users": [,
{
"email": "johnDoe#gmail.com",
"password": "blabala",
"firstname": "John",
"lastname": "Doe",
"address": "4 rue gay lussac",
"city": "Paris",
},
{
"email": "new email",
"password": "new password",
"firstname": "new firstname",
"lastname": "new lastname",
"address": "new address",
"city": "new city",
}
],
}
i'm currently working in nodejs using the writeFileSync() method from fs library.
My index.js looks like this :
server.post("/register", (req, res) => {
const {firstname, lastname, email, password,address, city} = req.body
if(firstname && lastname && email && password && address && city) {
try {
fs.readFile("db.json")
fs.writeFileSync(path.join(__dirname, "db.json"),JSON.stringify(req.body), {encoding: "utf-8"})
res.status(201).send({
message: "User created!"
})
} catch (error) {
res.status(500).send({
code: error.code,
message: error.message
})
}
}else{
res.status(500).send({
message: "Something wrong"
})
}
})
Need some suggestions please. Thks!!

Answer 1

I did almost the same thing as you long time ago, you have to extract the content of the file as a JSON Object, modify it and then write it stringifyied in your file.
I still have a snippet of what I've done in the past:
const getUsers = () => {
let users = fs.readFileSync(path.join(__dirname, '../workspace/.users.json'));
return JSON.parse(users);
};
const setUsers = (users) => {
let newUsersObject = JSON.stringify(users, null, 2);
fs.writeFileSync(path.join(__dirname, '../workspace/.users.json'), newUsersObject);
};
So with this two functions you can do things like:
//retrieve users
let userObject = getUsers();
//edit the first user (example)
userObject[0].firstname = "John";
userObject[1].lastname = "Doe";
//save the modified object
setUsers(userObject);