The append() method of the FormData interface appends a new value onto an existing key inside a FormData object, or adds the key if it does not already exist.
Optionalfilename: stringThe delete() method of the FormData interface deletes a key and its value(s) from a FormData object.
Returns an array of key, value pairs for every entry in the list.
OptionalthisArg: anyThe 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 getAll() method of the FormData interface returns all the values associated with a given key from within a FormData object.
The has() method of the FormData interface returns whether a FormData object contains a certain key.
Returns a list of keys in the list.
The set() method of the FormData interface sets a new value for an existing key inside a FormData object, or adds the key/value if it does not already exist.
Optionalfilename: stringReturns a list of values in the list.
The
FormDatainterface provides a way to construct a set of key/value pairs representing form fields and their values, which can be sent using the fetch(), XMLHttpRequest.send() or navigator.sendBeacon() methods. It uses the same format a form would use if the encoding type were set to "multipart/form-data".MDN Reference