The onformdata property of the GlobalEventHandlers mixin is the EventHandler for processing formdata events, fired 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. onformdata is available on HTMLFormElement.


target.onformdata = functionRef;


functionRef is a function name or a function expression. The function receives a FormDataEvent object as its sole argument.


// grab reference to form

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

// submit handler

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

  // construct a FormData object, which fires the formdata event
  new FormData(formElem);

// formdata handler to retrieve data

formElem.onformdata = (e) => {
  console.log('formdata fired');

  // Get the form data from the event object
  let data = e.formData;
  for (var value of data.values()) {

  // submit the data via XHR
  var request = new XMLHttpRequest();"POST", "/formHandler");


Specification Status Comment
HTML Living Standard
The definition of 'onformdata' in that specification.
Living Standard

Browser compatibility

BCD tables only load in the browser

See also