The FormDataEvent interface represents a formdata event — such an event is fired on an HTMLFormElement object after the entry list representing the form's data is constructed. This happens when the form is submitted, but can also be triggered by the invocation of a FormData() constructor.

This allows a FormData object to be quickly obtained in response to a formdata event firing, rather than needing to put it together yourself when you wish to submit form data via a method like fetch() (see Using FormData objects).

Event FormDataEvent



Creates a new FormDataEvent object instance.

Instance properties

Inherits properties from its parent interface, Event.


Contains the FormData object representing the data contained in the form when the event was fired.

Instance methods

Inherits methods from its parent interface, Event.


// grab reference to form

const formElem = document.querySelector("form");

// submit handler

formElem.addEventListener("submit", (e) => {
  // on form submission, prevent default

  console.log(form.querySelector('input[name="field1"]')); // FOO
  console.log(form.querySelector('input[name="field2"]')); // BAR

  // construct a FormData object, which fires the formdata event
  const formData = new FormData(formElem);
  // formdata gets modified by the formdata event
  console.log(formData.get("field1")); // foo
  console.log(formData.get("field2")); // bar

// formdata handler to retrieve data

formElem.addEventListener("formdata", (e) => {
  console.log("formdata fired");

  // modifies the form data
  const formData = e.formData;
  formData.set("field1", formData.get("field1").toLowerCase());
  formData.set("field2", formData.get("field2").toLowerCase());


HTML Standard
# the-formdataevent-interface

Browser compatibility

BCD tables only load in the browser

See also