How apply this method select option than submit submit must not apply without choose any option

Answer 1

https://developer.mozilla.org/en-US/docs/Web/API/HTMLSelectElement/selectedIndex

Answer 2

first off let's define the select as
<select name="category" required>
the first option is value=""
<option value="">select</option>
not value=" "
example in the code

https://code.sololearn.com/WAwcrS8rJj4r/?ref=app