FormData: append() method
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.
Note: This method is available in Web Workers.
Syntax
js
append(name, value)
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 string or
Blob
(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 string), when a
Blob
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.
Return value
None (undefined
).
Examples
js
formData.append("username", "Chris");
When the value is a Blob
(or a File
), you can specify its name with the filename
parameter:
js
formData.append("userpic", myFileInput.files[0], "chris.jpg");
As with regular form data, you can append multiple values with the same name:
js
formData.append("userpic", myFileInput.files[0], "chris1.jpg");
formData.append("userpic", myFileInput.files[1], "chris2.jpg");
If the value is not a string or a Blob
, append()
will convert it to a string automatically:
js
formData.append("name", true);
formData.append("name", 72);
formData.getAll("name"); // ["true", "72"]
Specifications
Specification |
---|
XMLHttpRequest Standard # dom-formdata-append |
Browser compatibility
BCD tables only load in the browser