FormData.

Theory. new FormData(form) collects every field of the form that has a name. You do not search for each field one by one: data.get("name") returns a value (string) or null.

Key rule: an unchecked checkbox is NOT in FormData at all — the key is missing. So data.get("paid") is null, not "false". A submit button without a name is not included either.

Small examples:

const data = new FormData(form); const name = data.get("name"); const rows = []; for (const [key, value] of data.entries()) rows.push(key + "=" + value); const text = rows.join(";");

The order follows the field order in the DOM. Fields without a name (id only) are invisible to FormData.

Common mistake: looking for id instead of name; expecting false for an unchecked checkbox; reading FormData outside a submit/click listener.