//!Module-ok importálása
const express = require('express'); //?npm install express
const session = require('express-session'); //?npm install express-session
const path = require('path');
const fs = require('fs');

const app = express();
const router = express.Router();
//!SQL Queries importálása
const db = require(path.join(__dirname + '/sql/db-queries'));

//!Multer
const multer = require('multer');
const storage = multer.diskStorage({
    destination: './uploads',
    filename: (request, file, callback) => {
        callback(null, file.originalname);
    }
});
const upload = multer({ storage: storage });

<!--Illetve a db-queries.js-ben-->
const mysql = require('mysql');

// math.js
function add(a, b) {
    return a + b;
}
module.exports = add;

// index.js
const add = require('./math');
console.log(add(2, 3)); // Kimenet: 5

<!--Egyszerre többet is tudunk exportálni-->
// utils.js
module.exports = {
appName: 'MyApp',
version: '1.0.0',
multiply: (a, b) => a * b,
users: ['Alice', 'Bob', 'Charlie']
};

// main.js
const utils = require('./utils');
console.log(utils.appName); // Kimenet: 'MyApp'
console.log(utils.version); // Kimenet: '1.0.0'
console.log(utils.multiply(2, 3)); // Kimenet: 6
console.log(utils.users); // Kimenet: ['Alice', 'Bob', 'Charlie']

function postMethodFetch(url, postObject) {
    return fetch(url, {
        method: 'POST',
        headers: {
        'Content-Type': 'application/json'
    },
    body: JSON.stringify(postObject)
})
    .then((response) => {
        if (!response.ok) {
        throw new Error(`Hiba: ${response.status}`);
    }
    return response.json();
    })
    .catch((error) => {
        throw new Error(`Hiba történt: ${error.message}`);
    });
}

Használata:
const url = url;
const postObject = {
    title: 'foo',
    body: 'bar',
    userId: 1
};
postMethodFetch(url, postObject)
    .then((data) => {
        console.log('Siker:', data);
    })
    .catch((error) => {
        console.error(error.message);
    });

function postMethodFetch(url, postObject) {
    return new Promise((resolve, reject) => {
        fetch(url, {
            method: 'POST',
            headers: {
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(postObject)
        })
        .then((response) => {
            if(!response.ok) {
                reject(`Hiba: ${response.status}`);
            }
            return response.json();
        })
        .then((data) => {
            resolve(data);
        })
        .catch((error) => {
            reject(`Hiba történt: ${error.message}`);
        });
    });
}

Használata:
const url = url; // Egy teszt API
const postObject = {
    title: 'foo',
    body: 'bar',
    userId: 1
};
postMethodFetch(url, postObject)
    .then((data) => {
        console.log('Sikeres válasz:', data);
    })
    .catch((error) => {
        console.error('Hiba történt:', error);
    });