Using variables or constants in nextjs api - rest

Question

I'm trying to use a constant in my API. This constant is an array where I can push or pop objects. I populate it through API calls. This is the code:
const washes = [];
export default async (req, res) => {
if(req.method === 'GET')
{
res.json({washes});
}
if(req.method === 'POST')
{
washes.push(req.body);
console.log(washes);
res.json({washes});
}
}
I make calls from the front-end to populate the array and to retrieve it. The problem is that, sometimes I get an empty array an sometimes I get the expected array. Or after a while I always get the empty array, like if it was restarted.
I deployed the application on Vercel.
Is there something I'm missing from the back-end functionality, or is it related to Vercel?. Last but not least is it a good practice to use variables or constants in back-end.?

Answer 1

You cant use an array as storage. You need to connect it to a database of sorts.
When you use this endpoint it will only retrieve the correct array sometimes, because it's stored in a temporary memory on the server.
Look into firebase if you easily want to setup up a project and store information in a database.
https://firebase.google.com/docs/web/setup
Another way is to use a .json file in the back-end
Read more here: https://jasonwatmore.com/post/2021/08/28/next-js-read-write-data-to-json-files-as-the-database
USER EXAMPLE
const fs = require('fs');
// users in JSON file for simplicity, store in a db for
production applications
let users = require('data/users.json');
export const usersRepo = {
getAll: () => users,
getById: id => users.find(x => x.id.toString() === id.toString()),
find: x => users.find(x),
create,
update,
delete: _delete
};
function create(user) {
// generate new user id
user.id = users.length ? Math.max(...users.map(x => x.id)) + 1 : 1;
// set date created and updated
user.dateCreated = new Date().toISOString();
user.dateUpdated = new Date().toISOString();
// add and save user
users.push(user);
saveData();
}
function update(id, params) {
const user = users.find(x => x.id.toString() === id.toString());
// set date updated
user.dateUpdated = new Date().toISOString();
// update and save
Object.assign(user, params);
saveData();
}
// prefixed with underscore '_' because 'delete' is a reserved word in javascript
function _delete(id) {
// filter out deleted user and save
users = users.filter(x => x.id.toString() !== id.toString());
saveData();
}
// private helper functions
function saveData() {
fs.writeFileSync('data/users.json', JSON.stringify(users, null, 4));
}