copy_table_as_csv.js

javascript:(function() {

  function clean(str) {
    return (str || '').replace(/\s+/g, ' ').trim();
  }

  function quote(str) {
    return '"' + str.replace(/"/g, '""') + '"';
  }

  function getCsv(table) {
    let csv = [];
    for (let row of table.querySelectorAll('tr')) {
      let csv_row = [];
      for (let cell of row.querySelectorAll('th, td')) {
        csv_row.push(quote(clean(cell.textContent)));
      }
      csv.push(csv_row.join(','));
    }
    return csv.join('\n');
  }

  for (let table of document.querySelectorAll('table')) {
    let c = document.createElement('button');
    c.style.margin = '10px 10px 10px 10px';
    c.style.padding = '5px 10px 5px 10px';
    c.style.background = '#fcc';
    c.style.color = 'black';
    c.style.border = "1px solid 'black'";
    c.innerHTML = 'Copy CSV into clipboard';
    let table_el = table;
    c.addEventListener('click', () => {
      let csv = getCsv(table_el);
      navigator.clipboard.writeText(csv).then(function() {
        alert('Table is copied into clipboard');
      }, function() {
        alert('Error');
      })
    });
    table.parentNode.insertBefore(c, table);
  }

}())

This is a bookmarklet which adds a button next to all <table>s for copying its content as a CSV.