Future<HttpRequest> postFormData(String url, Map<String, String> data, {bool withCredentials, String responseType, Map<String, String> requestHeaders, onProgress(ProgressEvent e)})

Makes a server POST request with the specified data encoded as form data.

This is roughly the POST equivalent of getString. This method is similar to sending a FormData object with broader browser support but limited to String values.

If data is supplied, the key/value pairs are URI encoded with Uri.encodeQueryComponent and converted into an HTTP query string.

Unless otherwise specified, this method appends the following header:

Content-Type: application/x-www-form-urlencoded; charset=UTF-8

Here's an example of using this method:

var data = { 'firstName' : 'John', 'lastName' : 'Doe' };
HttpRequest.postFormData('/send', data).then((HttpRequest resp) {
  // Do something with the response.
});

See also:

Source 

static Future<HttpRequest> postFormData(String url, Map<String, String> data,
    {bool withCredentials, String responseType,
    Map<String, String> requestHeaders,
    void onProgress(ProgressEvent e)}) {

  var parts = [];
  data.forEach((key, value) {
    parts.add('${Uri.encodeQueryComponent(key)}='
        '${Uri.encodeQueryComponent(value)}');
  });
  var formData = parts.join('&');

  if (requestHeaders == null) {
    requestHeaders = <String, String>{};
  }
  requestHeaders.putIfAbsent('Content-Type',
      () => 'application/x-www-form-urlencoded; charset=UTF-8');

  return request(url, method: 'POST', withCredentials: withCredentials,
      responseType: responseType,
      requestHeaders: requestHeaders, sendData: formData,
      onProgress: onProgress);
}