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 FormData.set and append() is that if the specified key already exists, FormData.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.

Note: This method is available in Web Workers.

Syntax

There are two versions of this method: a two and a three parameter version:

formData.append(name, value);
formData.append(name, value, filename);

Parameters

name
The name of the field whose data is contained in value.
value
The field's value. This can be a USVString or Blob (including subclasses such as File).
filename Optional
The filename reported to the server (a USVString), 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.

Note: If you specify a Blob as the data to append to the FormData object, the filename that will be reported to the server in the "Content-Disposition" header used to vary from browser to browser.

Returns

Void.

Example

The following line creates an empty FormData object:

var formData = new FormData(); // Currently empty

You can add key/value pairs to this using FormData.append:

formData.append('username', 'Chris');
formData.append('userpic', myFileInput.files[0], 'chris.jpg');

As with regular form data, you can append multiple values with the same name. For example (and being compatible with PHP's naming conventions by adding [] to the name):

formData.append('userpic[]', myFileInput.files[0], 'chris1.jpg');
formData.append('userpic[]', myFileInput.files[1], 'chris2.jpg');

This technique makes it simpler to process multi-file uploads because the resultant data structure is more conducive to looping.

Specifications

Specification Status Comment
XMLHttpRequest
The definition of 'append()' in that specification.
Living Standard Initial definition

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome Full support 7Edge Full support YesFirefox Full support 4
Notes
Full support 4
Notes
Notes Prior to Firefox 7, specifying a Blob as the data to append to the object, the filename reported in the Content-Disposition HTTP header was an empty string, resulting in errors on some servers. Starting with Firefox 7, the filename blob is sent.
IE Full support 10
Notes
Full support 10
Notes
Notes With the "Include local directory pass when uploading files to a server" option enabled, IE will change the filename inside the Blob on the fly. To have direct control of the sent filename, the developer should send the filename as the third parameter value, i.e. formData.append(name, value, filename).
Opera Full support 12Safari Full support 5WebView Android Full support 3
Notes
Full support 3
Notes
Notes XHR in Android 4.0 sends empty content for FormData with blob.
Chrome Android ? Edge Mobile Full support YesFirefox Android Full support 4
Notes
Full support 4
Notes
Notes Prior to Firefox 7, specifying a Blob as the data to append to the object, the filename reported in the Content-Disposition HTTP header was an empty string, resulting in errors on some servers. Starting with Firefox 7, the filename blob is sent.
Opera Android Full support 12Safari iOS ? Samsung Internet Android ?
append with filenameChrome Full support YesEdge Full support YesFirefox Full support 22IE Full support YesOpera ? Safari Full support YesWebView Android ? Chrome Android ? Edge Mobile ? Firefox Android Full support 22Opera Android ? Safari iOS ? Samsung Internet Android ?

Legend

Full support  
Full support
Compatibility unknown  
Compatibility unknown
See implementation notes.
See implementation notes.

See also

Document Tags and Contributors

Last updated by: ExE-Boss,