register user using json and local storage - reactjs

Question

I'm trying to create a webapp where a user can log in and register.
I have to store the user list locally, meaning no db is allowed, and I have a json file called "usersDB" instead.
I thought about creating the register using append or push but it doesn't seem to work, any idea how to add a new user?
my code:
let userFile = require ("./users.json");
const express = require("express");
const {v4: uuidv4} = require('uuid');
const port = process.env.PORT || 3005;
const app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: true}));
app.use(express.json());
app.get("/users",((req, res) => {
res.status(200).send(userFile);
}))
app.get("/products",((req, res) => {
res.status(200).send(productFile);
}))
app.post(`/register`, async (req, res, next) => {
if(req.body.username.valueOf()===undefined||req.body.password.valueOf()===undefined ){
res.err("undefined");
}
let id = genarateUuid();
// createUser
//add to db
let user = {id:id,username:req.body.username,password:req.body.password,cart:[],purchases:[],login:[],sessions:[],isAdmin: false};
userFile.append(user); //doesn't seem to work
res.status(200).json(user);
}
)

Answer 1

Looks like you're using node and express. You'll need to use fs to read/write to files (and I like to use path in combination with fs to build the file paths).
To write to a file (Assuming users.json contains an array of user objects):
const fs = require('fs');
app.post('/register', async (req, res, next) => {
// build user variable...
// read current file contents
const filePath = path.join(process.cwd(), 'users.json');
const fileData = fs.readFileSync(filePath);
const data = JSON.parse(fileData);
// append the new user
data.push(user);
// write the file back to users.json
fs.writeFileSync(filePath, JSON.stringify(data));
res.status(200).json(user);
});
To read from that file:
app.get('/users', (req, res) => {
// read current file contents
const filePath = path.join(process.cwd(), 'users.json');
const fileData = fs.readFileSync(filePath);
const data = JSON.parse(fileData);
res.status(200).json(data);
});
You could also refactor that code a bit more to avoid code repeat.
For instance, make a function called getUsers:
const getUsers = (filePath) => {
const fileData = fs.readFileSync(filePath);
const data = JSON.parse(fileData);
return data;
}
Hope this helps you out!