UserScript for converting everything in BZWBK panel into PLN, keeping it here so I won't loose it.

BZWBK_online_portfolio_currency_converter.js

// ==UserScript==
// @name         BZWBK Currency Converter
// @version      0.1
// @description  computes currency in BZWBK online panel to display everything in PLN
// @author       You
// @require      https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.6.15/browser-polyfill.min.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/babel-core/5.6.15/browser.min.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.4/jquery.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/money.js/0.2.0/money.min.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/accounting.js/0.4.1/accounting.min.js
// @match        https://www.centrum24.pl/centrum24-web/portfolio
// ==/UserScript==

/* jshint ignore:start */
var inline_src = (<><![CDATA[
    /* jshint ignore:end */
    /* jshint esnext:true */

    GM_xmlhttpRequest({
        method: "GET",
        url: "http://api.fixer.io/latest",
        onload: ({ response }) => {
            fx.base = 'EUR';
            fx.rates = JSON.parse(response).rates;

            const currencies = [ 'GBP', 'USD', 'EUR' ];

            const parseMoney = (moneyString) => {
                return parseFloat(moneyString
                                  .replace(/\s+/g, '')
                                  .replace(',', '.'));
            };

            const formatMoney = (moneyNumber) => {
                return accounting.formatMoney(
                    moneyNumber,
                    {
                        symbol:   'PLN',
                        format:   '%v %s',
                        thousand: ' ',
                        decimal:  ','
                    }
                );
            };


            $("td.money").each((i, item) => {
                const $item = $(item);
                const text  = $item.text();

                if (currencies.some(currency => text.indexOf(currency) >= 0)) {
                    const currency       = currencies.filter(currency => text.indexOf(currency) >= 0);
                    const parsedMoney    = parseMoney(text);
                    const convertedMoney = fx.convert(parsedMoney, { from: currency, to: 'PLN' }).toFixed(2);

                    $item.text(formatMoney(convertedMoney));
                    $item.append(`<span style="font-size: 11px">${text}</span>`);
                }
            });
        }
    })

/* jshint ignore:start */
]]></>).toString();
var c = babel.transform(inline_src);
eval(c.code);
/* jshint ignore:end */