Problem with checkbox array return data

Hi guys,
I’m using the function to return my form:

let formData = self.$f7.form.convertToData('#t4Form');

So far it is working, however, I am having a problem to return values that are type array, at that moment it would be the input checkbox that I have which is an array.
Example html:
<input type="checkbox" name="extras[]" value="1"> <input type="checkbox" name="extras[]" value="2"> <input type="checkbox" name="extras[]" value="3"> ...

The result is:
Field === extras ||| Value === undefined

How resolve it?