HTMLFormElement: formdata event

The formdata event fires 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.

General info

Bubbles	No
Cancelable	No
Interface	`FormDataEvent`
Event handler property	`GlobalEventHandlers.onformdata`

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 gets modified by the formdata event
  formData.set('field1', formData.get('field1').toLowerCase());
  formData.set('field2', formData.get('field2').toLowerCase());
});

The onformdata version would look like this:

formElem.onformdata = (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

Specification
HTML Standard # event-formdata

Browser compatibility

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