The FormData interface provides 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. It uses the same format a form would use if the encoding type were set to "multipart/form-data".
The FormData.entries() method returns an iterator allowing to go through all key/value pairs contained in this object. The key of each pair is a USVString object; the value either a USVString, or a Blob.
The get() method of the FormData interface returns the first value associated with a given key from within a FormData object. If you expect multiple values and want all of them, use the getAll() method instead.
The FormData object lets you compile a set of key/value pairs to send using XMLHttpRequest. 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.