index.md

title	slug	page-type	browser-compat
FormDataEvent	Web/API/FormDataEvent	web-api-interface	api.FormDataEvent

{{APIRef("DOM")}}

The FormDataEvent interface represents a formdata event — such an event is fired on an {{domxref("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 {{domxref("FormData.FormData", "FormData()")}} constructor.

This allows a {{domxref("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 {{domxref("fetch()")}} (see Using FormData objects).

{{InheritanceDiagram}}

Constructor

• {{domxref("FormDataEvent.FormDataEvent","FormDataEvent()")}}
  • : Creates a new FormDataEvent object instance.

Instance properties

Inherits properties from its parent interface, {{domxref("Event")}}.

• {{domxref("FormDataEvent.formData")}}
  • : Contains the {{domxref("FormData")}} object representing the data contained in the form when the event was fired.

Instance methods

Inherits methods from its parent interface, {{domxref("Event")}}.

Examples

// grab reference to form

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

// submit handler

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

  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());
});

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{domxref("fetch()")}}
• {{domxref("FormData")}}
• Using FormData objects
• {{HTMLElement("Form")}}