steam_annual_bill.js

const year = '2019';

Array.from(document.querySelectorAll('.wallet_table_row'))
  .filter(tr => {
    return (
      tr.querySelector('.wht_type div:first-child').textContent === '购买' &&
      tr.querySelector('.wht_date').textContent.indexOf(year) !== -1
    );
  })
  .map(tr =>
    tr
      .querySelector('.wht_total')
      .textContent.replace('¥', '')
      .trim()
  )
  .reduce((s, i) => s + parseInt(i, 10), 0);