JSFiddle - React, Tailwind, and code Playground
HTML
<select class="form-control" required name="article">
<option value="Coca Cola">Coca Cola</option>
</select>
<input class="form-control number-input" value="" name="qty" type="text">
<select class="form-control" required name="article">
<option value="Jupi">Jupi</option>
</select>
<input class="form-control number-input" value="" name="qty" type="text">
<select class="form-control" required name="article">
<option value="Fanta">Fanta</option>
</select>
<input class="form-control number-input" value="" name="qty" type="text">
JavaScript
var invoiceNumber = 1;
var articles = $('[name~=article]').map(function () {
return $(this).val()
}).get();
var qty = $('[name~=qty]').map(function () {
return $(this).val()
}).get();