kufar.js

const selectors = [
    "[class*=styles_price--main__]",
    "[class*=styles_price__]",
    "[class*=styles_main]",
    "[class*=styles_discountPrice]",
    ".account_ads__price",
].join(",");

let rate;

(async () => {
    const response = await fetch("https://api.nbrb.by/exrates/rates/431");
    const data = await response.json();
    rate = data["Cur_OfficialRate"];
})();

function addConversion() {
    let elements = document.querySelectorAll(selectors);

    if (elements) {
        for (let element of elements) {
            let price = convertToDollars(element);

            if (!isNaN(price)) {
                element.innerHTML += "<span> " + price.toFixed(2) + " $" + "</span>";
            }
        }
    }
}

function convertToDollars(element) {
    let text = element.textContent;

    if (!text.includes("%") && !text.includes("$") && text.includes("р.")) {
        let price = parseFloat(text.replace(/[^0-9.]/g, ""));
        let conversion = price / rate;
        return conversion;
    }
    return NaN;
}

const observer = new window.MutationObserver(() => {
    if (rate) {
        addConversion();
    }
});

observer.observe(document, {
    subtree: true,
    attributes: true,
});