FormData.append()

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.

The difference between set() and append() is that if the specified key already exists, set() will overwrite all existing values with the new one, whereas append() will append the new value onto the end of the existing set of values.

Inputs: name The name of the field whose data is contained in value. value The field’s value. This can be a string or Blob (including subclasses such as File). If none of these are specified the value is converted to a string. filename The filename reported to the server (a string), when a Blob or File is passed as the second parameter. The default filename for Blob objects is “blob”. The default filename for File objects is the file’s filename.