Validate Dates, Descriptions, and Amounts

Do not let the form send obviously invalid values. Put the reusable rules in client/src/lib/finance.js.

The final project uses real calendar validation and a money parser that accepts at most two decimal places.

export function isValidDateOnly(value) {
  if (typeof value !== "string" || !/^\d{4}-\d{2}-\d{2}$/.test(value)) return false;
  const [year, month, day] = value.split("-").map(Number);
  const date = new Date(Date.UTC(year, month - 1, day));
  return (
    date.getUTCFullYear() === year &&
    date.getUTCMonth() === month - 1 &&
    date.getUTCDate() === day
  );
}

Test it

Try an empty description, a zero amount, 84.567, and an invalid calendar date such as February 30. Each should produce a clear validation message.

Checkpoint

The form rejects malformed input before making the API request.