It calculates total paid. Run on 'https://booklive.jp/my/top'

booklivepaid.js

!Number.prototype.padLeft && Object.defineProperty(Number.prototype, "padLeft", {
  value(n, s = " ") {
    return (Array(n).join(s) + this).slice(-n);
  }
});

main();

function main() {
  const now = new Date;
  const startYear = now.getFullYear();
  const startMonth = now.getMonth() + 1;
  
  const least = prompt("何年まで遡りますか？", startYear);
  if (!/^[0-9]{4}$/.test(least)) {
    return alert("半角4文字の西暦で入力してください。");
  }
  
  const history = Object.create(null);
  const tasks = [];
  
  let paid = 0;
  
  for (let y = startYear + 1; --y >= least;) {
    for (let m = (y === startYear ? startMonth : 12) + 1; --m > 0;) {
      const task = monthSum(y, m).then(price => {
        history[`${y.padLeft(4)}年${m.padLeft(2)}月`] = price.toLocaleString() + "円";
        paid += price;
      });
      tasks.push(task);
    }
  }
  Promise.all(tasks).then(_ =>
    console.info(`合計: ${paid.toLocaleString()}円`, sortObjectByKey(history)));
}

function monthSum(year, month) {
  return request(`/my/product?year=${year}&month=${month}`)
  .then(doc => {
    const nodes = doc.querySelectorAll('[id^="myproduct_display"]');

    if (nodes.length) {
      return Array.from(nodes, e => e.textContent.trim())
        .filter(text => text.endsWith("円"))
        .map(price => parseInt(price.split(",").join(""), 10))
        .reduce((a, b) => a + b);
    }
    else return 0;
  });
}

function request(url) {
  return fetch(url, { credentials: "include" }).then(res => res.text())
  .then(text => {
    const range = document.createRange();
    const dom = range.createContextualFragment(text);
    try {
      return dom;
    }
    finally { range.detach(); }
  });
}

function sortObjectByKey(obj) {
  return Object.keys(obj).sort()
    .reduce((acc, key) => Object.assign(acc, {[key]: obj[key]}), Object.create(null));
}