table-to-csv.js

const csvEscape = function() {
  const map = {
    ";": ",",
    "\n": "\\n"
  };
  const replacerRe = /./gsm;
  const replacer = x => `\\x${x.charCodeAt(0).toString(16).padStart(2, 0)}`;
  const escaped = Object.keys(map).map(x => x.replace(replacerRe, replacer));
  const escapeRe = new RegExp(escaped.join("|"), "g");
  const escape = x => map[x];
  return el => {
    const span = el.getAttribute("colspan") | 0;
    const escaped = el.textContent.trim().replace(escapeRe, escape);
    return span < 2 ? escaped : Array(span).fill(escaped).join(";");
  };
}();

function processRow({ children: row }) {
  const length = row.length;
  if (!length) return "";
  const str = length > 50 ? Array(length) : [];
  str[0] = csvEscape(row[0]);
  for (let i = 1; i < length; ++i) {
    str[i] = `;${csvEscape(row[i])}`;
  }
  return str.join("");
}

function processHead(table, target) {
  const { tHead } = table;
  if (!tHead) return;
  const { rows } = tHead;
  switch (rows.length) {
    case 0: return;
    case 1: break;
    default: throw new RangeError("can't have more than one head row");
  }
  target.push(processRow(rows[0]));
}

function processBodies(table, target) {
  for (const body of table.tBodies) {
    for (const row of body.children) {
      if (row.tagName === "TR") {
        target.push(processRow(row));
      }
    }
  }
}

function processFoot(table, target) {
  const { tFoot } = table;
  if (!tFoot) return;
  for (const row of tFoot.rows) {
    target.push(processRow(row));
  }
}

export default function tableToCsv(table) {
  if (table == null || table.tagName !== "TABLE") {
    throw new TypeError("invalid argument");
  }
  const result = [];
  processHead(table, result);
  processBodies(table, result);
  processFoot(table, result);
  return result.join("\n");
}