Handling Forms & User Input

form.addEventListener('formdata', e => {
  const formData = e.formData;
  formData.append('timestamp', Date.now());
  formData.delete('private');
});

When the form is created
When FormData is constructed
The 'formdata' event fires when a FormData object is constructed from a form element. This allows: 1) Modifying form data before it's used, 2) Adding additional fields programmatically, 3) Removing sensitive data, 4) Transforming values, 5) Handling dynamic form fields. It's particularly useful when you need to modify form data consistently across multiple submission methods or when using FormData for different purposes.
Before form submission
After form validation