cambio-dia.js

const request = require('request-promise-native');
const cheerio = require('cheerio');

const scrap = async (url, selector) => {
  let html;
  try {
    html = await request(url);
  } catch (err) {
    console.error(`Url no encontrada: ${url}`);
    return '';
  }

  const $ = cheerio.load(html);
  const valor = $(selector).text().trim();
  return valor;
};

const URL_DOLAR_SUNAT = 'http://www.sunat.gob.pe/cl-at-ittipcam/tcS01Alias';
const CSS_SELECTOR = '[class=\'class="form-table"\'] tr:last-child td:nth-last-child(2)';

const cambioDolarDia = async () => {
  let valor = await scrap(URL_DOLAR_SUNAT, CSS_SELECTOR);
  valor = parseFloat(valor);
  valor = (Math.trunc(valor * 10) / 10) - 0.2;
  return valor;
};

(async () => {
  console.log(await cambioDolarDia());
})();