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
orBlob
(including subclasses such asFile
). If none of these are specified the value is converted to a string. filename
Optional- The filename reported to the server (a
USVString
), when aBlob
orFile
is passed as the second parameter. The default filename forBlob
objects is "blob". The default filename forFile
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.
If the sent value is different than String or Blob it will be automatically converted to String:
formData.append('name', true); formData.append('name', 74); formData.append('name', 'John'); formData.getAll('name'); // ["true", "74", "John"]
Specifications
Specification | Status | Comment |
---|---|---|
XMLHttpRequest The definition of 'append()' in that specification. |
Living Standard | Initial definition |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
append | Chrome Full support 7 | Edge Full support 12 | Firefox
Full support
4
| IE
Full support
10
| Opera Full support 12 | Safari Full support 5 | WebView Android
Full support
3
| Chrome Android Full support 18 | Firefox Android
Full support
4
| Opera Android Full support 12 | Safari iOS Full support 5 | Samsung Internet Android Full support 1.0 |
append with filename | Chrome Full support Yes | Edge Full support 12 | Firefox Full support 22 | IE Full support Yes | Opera ? | Safari Full support 9 | WebView Android Full support Yes | Chrome Android Full support Yes | Firefox Android Full support 22 | Opera Android ? | Safari iOS Full support 9 | Samsung Internet Android Full support Yes |
Legend
- Full support
- Full support
- Compatibility unknown
- Compatibility unknown
- See implementation notes.
- See implementation notes.