index.js

require('dotenv').config();
const {performance} = require('perf_hooks');
const axios = require("axios");
const cheerio = require("cheerio");
const express = require('express');
const app = express();
const cors = require('cors');
app.use(cors());
const port = process.env.NODE_PORT
const explorerUrl = process.env.NODE_EXPLORER_URL;
const tokenAddress = process.env.NODE_TOKEN_ADDRESS;

if (!explorerUrl) throw "explorerUrl: undefined";
if (!tokenAddress) throw "explorerUrl: undefined";
if (!port) throw "port: undefined";


const numbers = '0123456789';

async function scrapeData(url) {
    try {
        const {data} = await axios.get(url);

        const $ = cheerio.load(data);

        const holders = $("div.mr-3").text();

        let holdersNumber = '';
        for (let i = 0; i < holders.length; i++)
            if (numbers.includes(holders.charAt(i)))
                holdersNumber = holdersNumber + holders.charAt(i);


        //console.log(holdersNumber);
        return holdersNumber;

    } catch (err) {
        console.error(err.message);
    }
}

let lastNumber;
let lastChecked;
app.get('/', async (req, res) => {
    const url = `${explorerUrl}/token/${tokenAddress}`;

    //console.log('received request')
    if (!lastNumber || performance.now() - lastChecked > 10000) { // if 10 sec have passed let refreshthe data we have
        lastNumber = await scrapeData(url);
        lastChecked = performance.now();
        //console.log('called backend')
    }
    res.send(lastNumber);
})

const chains = {
    bsc: 'https://bscscan.com',
    avax: 'https://snowtrace.io',
    eth: 'https://etherscan.io',
    kovan: 'https://kovan.etherscan.io',
    polygon: 'https://polygonscan.com',
}

const lastChecks = {};
const lastHolders = {};
app.get('/universal/:token/:network', async (req, res) => {
    const chain = chains[req.params.network];

    const url = `${chain}/token/${req.params.token}`;

    if (!lastHolders[url]  || performance.now() - lastChecks[url] > 10000) { // if 10 sec have passed let refreshthe data we have
        lastHolders[url] = await scrapeData(url);
        lastChecks[url] = performance.now();
        //console.log('called backend')
    }
    //const holders= await scrapeData(url);

    console.log(lastHolders[url])
    res.send(lastHolders[url]);
})

app.listen(port, () => {
    console.log(`App listening at http://localhost:${port}`)
})

function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}