Long & McQuade is having their blowout sale this weekend which means it's time for me to waste money again

long-mcquade-deal-finder.js

// This script finds the best deals from Long & McQuade's annual
// blowout sale and sorts them within their respective categories.
//
// USAGE:
// 1. Navigate to http://promo.long-mcquade.com/SaleFlyer.php
// 2. Select your nearest location under "View Other Locations' Flyers Here"
// 3. Open your browser's Javascript console
// 4. Paste the contents of this file into the console
// 5. Optionally, replace the value of ONLY_SHOW_DEALS_BELOW_THIS_FRACTION_OF_THE_ORIGINAL_COST
// 6. Optionally, replace the value of I_WILL_NOT_EVEN_CONSIDER_ANYTHING_THAT_COSTS_OVER
// 7. Hit enter

// Change these values to suit your needs.
// Reminder: you don't need anything from this sale.
const ONLY_SHOW_DEALS_BELOW_THIS_FRACTION_OF_THE_ORIGINAL_COST = 1 / 2;  // All valid values between 0 and 1.
const I_WILL_NOT_EVEN_CONSIDER_ANYTHING_THAT_COSTS_OVER = 200.00;  // Pinky promise!

const parsePrice = price => price.startsWith('$') && parseFloat(price.slice(1).replace(/,/g, ''));
Array.from(document.querySelectorAll('tbody tr'))
  .map(tr => {
    const cells = tr.querySelectorAll('td');
    const originalPrice = parsePrice(cells[cells.length - 2].textContent);
    const salePrice = parsePrice(cells[cells.length - 1].textContent);
    const isPriceRow = typeof originalPrice === 'number' && typeof salePrice === 'number';
    const deal = isPriceRow && salePrice / originalPrice;
    const parent = tr.parentNode;
    parent.removeChild(tr); // Eek! Side effect!
    return {
      deal,
      element: tr,
      show: isPriceRow && salePrice < I_WILL_NOT_EVEN_CONSIDER_ANYTHING_THAT_COSTS_OVER && deal <= ONLY_SHOW_DEALS_BELOW_THIS_FRACTION_OF_THE_ORIGINAL_COST,
      parent,
    };
  })
  .filter(row => row.show)
  .sort((a, b) => a.deal > b.deal)
  .forEach(({deal, element, parent}) => {
    const td = document.createElement('td');
    td.textContent = `${Math.floor((1 - deal) * 100)}% off`;
    element.append(td);
    parent.append(element);
  });