FormData.set

The set() method of the FormData interface sets a new value for an existing key inside a FormData object, or adds the key/value if it does not already exist.

The difference between set() and FormData.append is that if the specified key does already exist, set() will overwrite all existing values with the new one, whereas FormData.append will append the new value onto the end of the existing set of values.

Syntax

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

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

Parameters

name

The name of the field whose data is contained in value.

value

The field's value. In the two parameter version this is a USVString, or if it is not, it is converted to a string. In the three parameter version this can be a Blob, File, or a USVString. If none of these are specified the value is converted to a string.

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".

Example

The following line creates an empty FormData object:

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

You can set key/value pairs on this using FormData.set:

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

Specifications

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

Browser compatibility

See also

• XMLHTTPRequest
• Using XMLHttpRequest
• Using FormData objects
• <form>