furusato-tax.jpの表示金額に2割の表示を追加するGreasemonkeyスクリプト

furusato-tax.jp: price * 0.2.user.js

// ==UserScript==
// @name        furusato-tax.jp: price * 0.2
// @namespace   furusato-tax.jpの表示金額に2割の表示を追加する
// @match       https://www.furusato-tax.jp/*
// @grant       none
// @version     1.0
// @author      -
// @description 2021/8/8 12:08:48
// @run-at          document-end
// ==/UserScript==
// 表示する金額の割合
const PRICE_RATE = 0.2;
/**
 * Parse a localized number to a float.
 * @param {string} stringNumber - the localized number
 * @param {string} locale - [optional] the locale that the number is represented in. Omit this parameter to use the current locale.
 */
function parseLocaleNumber(stringNumber, locale) {
    var thousandSeparator = Intl.NumberFormat(locale).format(11111).replace(/\p{Number}/gu, '');
    var decimalSeparator = Intl.NumberFormat(locale).format(1.1).replace(/\p{Number}/gu, '');

    return parseFloat(stringNumber
        .replace(new RegExp('\\' + thousandSeparator, 'g'), '')
        .replace(new RegExp('\\' + decimalSeparator), '.')
    );
}
const update = () => {
  const prices = document.querySelectorAll(".card-product__price, .goods--slide__price, .goods-col_price");
  for (priceNode of prices) {
    if(priceNode.dataset.gmModified){
      continue;
    }
    const originalValue = parseLocaleNumber(priceNode.textContent.trim(), "ja-JP");
    if(originalValue){
      const value2wari = originalValue * PRICE_RATE;
      const value2Format = Intl.NumberFormat("ja-Jp").format(value2wari);
      priceNode.textContent += ` (${value2Format}円)`;
      priceNode.dataset.gmModified = 1;
    }
  }
  // content 
  const mainPrice = document.querySelector(".basicinfo_price");
  if(mainPrice && !mainPrice.dataset.gmModified) {
    const orignalValueMatch = mainPrice.textContent.match(/[\d,]+\s{0,5}円/);
    const originalValue = parseLocaleNumber(orignalValueMatch[0].replace(/\s/g, ""), "ja-JP");
    if(originalValue){
      const value2wari = originalValue * PRICE_RATE;
      const value2Format = Intl.NumberFormat("ja-Jp").format(value2wari);
      mainPrice.append(document.createTextNode(`(${value2Format}円)`));
      mainPrice.dataset.gmModified = 1;
    }
  }
}
update();

const observer = new MutationObserver((mutations) => {
    update();
});
observer.observe(document.body, { childList: true, subtree:true });