server.js

const express = require('express');
const SparqlClient = require('sparql-http-client');
const cors = require('cors');
const app = express();
let fetchedData = [];

app.listen(8000, () => {
    console.log('Server is running...');
})

app.get("/", async function (req, res) {
    res.header('Access-Control-Allow-Origin', '*');
    res.send({
        Info: "Server is running...",
    })
})

app.get("/getdata", async function (req, res) {
    res.header('Access-Control-Allow-Origin', '*');
    asyncCallToLoadData.then(function () {
        res.send({
            data: fetchedData,
        })
    }).catch(function (error) {
        res.status(500).json({ Error: 'Internal server error' });
    });
})

let asyncCallToLoadData = new Promise(async function (Resolve, Reject) {
    try {
        //console.log('Data call initiated!');
        const client = new SparqlClient({ endpointUrl: 'http://localhost:3030/dataset/' });
        const stream = await client.query.select('PREFIX owl: <http://www.w3.org/2002/07/owl#>\
                        select distinct  ?subject ?predicate ?object {\
                        ?subject a owl:Class; \
                        ?predicate ?object \
                        FILTER(!isBlank(?subject))}');

        //console.log('Data stream loaded!');

        stream.on('data', row => {
            //console.log(`${row.subject.value} + ' # ' + ${row.predicate.value} + ' # ' + ${row.object.value}`);
            fetchedData.push({ subject: row.subject.value, predicate: row.predicate.value, object: row.object.value });
        })
        stream.on('end', function () {
            Resolve();
        })
    } catch (error) {
        //console.error("Error Message: " + error.message);
        Reject("Error Message: " + error.message);
    }
});

app.use(cors());