How to append array to FormData and send via AJAX with JavaScript?

To append array to FormData and send via AJAX with JavaScript, we create a FormData object.

For instance, we write

const formData = new FormData();
const arr = ["this", "is", "an", "array"];

for (const a of arr) {
  formData.append("arr[]", a);
}

to loop through the arr array items with a for-of loop.

In the loop, we call formData.append with the key and the value to append to the form data object.