XMLHttpRequest Level 2 adds support for the new FormData interface. FormData
objects provide a way to easily construct a set of key/value pairs representing
form fields and their values, which can then be easily sent using the
XMLHttpRequest send() method.
XMLHttpRequest Level 2 adds support for the new FormData interface. FormData objects provide a way to easily construct a set of key/value pairs representing form fields and their values, which can then be easily sent using the XMLHttpRequest send() method.
MDN