Web/API/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.

Note: This method is available in Web Workers.

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. This can be a USVString or Blob (including subclasses such as File). 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". 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.

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');

If the sent value is different than String or Blob it will be automatically converted to String:

formData.set('name', 72);
formData.get('name'); // "72"

Specifications

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

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`set`	Chrome Full support 50	Edge Full support 18	Firefox Full support 39	IE No support No	Opera Full support 37	Safari Full support 11	WebView Android Full support 50	Chrome Android Full support 50	Firefox Android Full support 39	Opera Android Full support 37	Safari iOS Full support 11	Samsung Internet Android Full support 5.0

Legend

Full support: Full support
No support: No support