Using FormData Objects - Web APIs | MDN

The FormData object lets you compile a set of key/value pairs to send using the Fetch or XMLHttpRequest API. It is primarily intended for use in sending form data, but can be used independently from forms in order to transmit keyed data. The transmitted data is in the same format that the form's submit() method would use to send the data if the form's encoding type were set to multipart/form-data.

[ginpei]

form要素配下の入力内容をまとめてあれこれできるやつ。XHRと連携してフォーム送信を仮想実行できる。