(6 kyu) Easy Balance Checking.js

// #1 Original solution
function balance(book) {
  const lines = book.split`\n`; // take each lines from a book
  const budget = parseInt(lines.shift()); // store an Original Balance
  // we need to clear all record from special characters, so
  // a helper function: remove special characters
  // (only alphanums and a '.' are allowed)
  const filterChars = (r) => r.split``.filter((a) => /[\w,\.]/.test(a)).join``;
  // take each line from a book
  const expences = lines
    // split each line by a whitespace
    .map((record) => record.split` `)
    // store only not empty lines
    .filter((r) => r[2])
    // for that lines take 3 records
    .map(
      (r) => [
        r[0], // take a record's number, it's a string
        filterChars(r[1]), // remove special chars from a title
        parseFloat(filterChars(r[2])),
      ], // remove special chars from a price
      // and take a float number value
    );
  let balance = budget; // use for a dynamic budget
  let totalExpense = 0;
  const calcLines = expences.map((r) => {
    balance -= r[2]; // calculate current balance
    totalExpense += r[2]; // calculate a Total expense
    // for a result formatted line
    return `${r[0]} ${r[1]} ${r[2].toFixed(2)} Balance ${balance.toFixed(2)}`;
  });
  // return all records as a text
  // Original balance
  return (
    `Original Balance: ${budget.toFixed(2)}\r\n` +
    // join all formatted into a one string
    calcLines.join('\r\n') +
    '\r\n' +
    // add a Total expense
    `Total expense  ${totalExpense.toFixed(2)}\r\n` +
    // and calculate an Average expense
    `Average expense  ${(totalExpense / calcLines.length).toFixed(2)}`
  );
}

// #2 Optimized solution
function balance(book) {
  let [budget, ...lines] = book
    .trim()
    .replace(/[^a-z0-9\s.]+/gi, '')
    .replace(/\s{2,}/g, (m) => m[0])
    .split(/\n/);

  let totalExpense = 0;
  const calcLines = lines.map((r) =>
    r.replace(/\S+$/g, (r) => {
      totalExpense += parseFloat(r);
      return `${parseFloat(r).toFixed(2)} Balance ${(
        budget - totalExpense
      ).toFixed(2)}`;
    }),
  );

  return (
    `Original Balance: ${parseFloat(budget).toFixed(2)}\r\n` +
    calcLines.join('\r\n') +
    '\r\n' +
    `Total expense  ${totalExpense.toFixed(2)}\r\n` +
    `Average expense  ${(totalExpense / calcLines.length).toFixed(2)}`
  );
}