It would be great if the example on the page
https://getform.io/docs/using-ajax/sending-submissions-with-ajax
would be also available in vanilla js. I don’t use jQuery in my projects.
https://developer.mozilla.org/en-US/docs/Learn/Forms/Sending_forms_through_JavaScript#Using_XMLHttpRequest_and_the_FormData_object (solution see below “Using FormData bound to a form element”). There is also the possibility to use fetch() but this isn’t as wells supported as the solution mentioned above.