Building a FormData Object Manually

You can populate a FormData object by calling the object's append() method for each field you want to add, passing in the field's name and value. The value can be a string, for text fields, or a Blob, for binary fields, including File objects.

In the following example, we send data as a form submission when the user clicks a button:

async function sendData(data) {
  // Construct a...