append method

void append(
  1. String key,
  2. dynamic value
)

Appends a new value onto an existing key inside a FormData object, or adds the key if it does not already exist.

To append File with additional settings like: filename, you can use appendFile method or pass FileField to append method.

Implementation

void append(String key, dynamic value) {
  ArgumentError.checkNotNull(key, 'key');

  if (value is File) {
    appendFile(key, value);
  } else if (value is num || value is bool) {
    _addEntry(key, value.toString());
  } else if (value is String || value is FileField || value == null) {
    _addEntry(key, value);
  } else {
    throw ArgumentError.value(
      value,
      'value',
      'Type ${value.runtimeType} is not valid form data value type.\n'
          'FormData supports: File, FileField, String, double, int, bool.',
    );
  }
}