crnc/x/currency-tools/download-exchange-rates.js

currency conversion and functionality for the web

import { requestXml } from "../toolbox/request-xml.js";
import { filterOutCurrenciesNotSupportedByBankOfCanada } from "./bank-of-canada/supported-currencies.js";
/**
 * Download exchange rates
 * - from bank of canada valet service https://www.bankofcanada.ca/valet/docs
 */
export async function downloadExchangeRates({ currencies, }) {
    currencies = filterOutCurrenciesNotSupportedByBankOfCanada(currencies);
    const canadian = "CAD";
    const nonCanadianOnly = (currency) => currency !== canadian;
    const toBankOfCanadaSeries = (currency) => `FX${currency}${canadian}`;
    const series = currencies
        .filter(nonCanadianOnly)
        .map(toBankOfCanadaSeries)
        .join(",");
    const url = `https://www.bankofcanada.ca/valet/fx_rss/${series}`;
    const xml = await requestXml(url);
    const exchangeRateElements = Array.from(xml.querySelectorAll("exchangeRate"));
    const rawRates = exchangeRateElements.map(element => {
        const value = parseFloat(element.querySelector("value").textContent);
        const currency = element.querySelector("targetCurrency").textContent;
        return { currency, value };
    });
    const exchangeRates = {};
    exchangeRates["CAD"] = 1.0;
    for (const rate of rawRates)
        exchangeRates[rate.currency] = 1 / rate.value;
    return { exchangeRates };
}
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