Bookmarklet to make tables to be todo lists

bookmarklet.js

//javascript:
(() => {
  const hash = str => {
    let hash = 0,
      chr;
    for (let i = 0; i < str.length; i++) {
      chr = str.charCodeAt(i);
      hash = (hash << 5) - hash + chr;
    }
    return btoa(hash.toFixed(0));
  };
  const key = "____done-work";
  const load = () => {
    let result;
    try {
      result = JSON.parse(localStorage.getItem(key));
    } catch (e) {
      console.error(e);
    } finally {
      return result || {};
    }
  };
  const save = data => {
    localStorage.setItem(key, JSON.stringify(data));
  };
  const start = () => {
    const data = load();
    const tables = document.querySelectorAll("table");
    for (const table of Array.from(tables)) {
      const rows = table.querySelectorAll("tr");
      for (const row of Array.from(rows)) {
        const rowKey = hash(row.textContent);
        const checked = !!data[rowKey];
        addCheckbox(row, data, rowKey, checked);
      }
    }
  };
  const addCheckbox = (row, data, rowKey, checked) => {
    const checkbox = document.createElement("input");
    checkbox.setAttribute("type", "checkbox");
    checkbox.checked = checked;
    checkbox.addEventListener("change", () => {
      if (!checkbox.checked) {
        delete data[rowKey];
      } else {
        data[rowKey] = true;
      }
      save(data);
    });
    const td = document.createElement("td");
    td.appendChild(checkbox);
    row.appendChild(td);
  };
  start();
})();