<script>
        let attributes_added = [];

        function add_attribute() {

            let id = document.getElementById('attributes').value;
            let value = document.getElementById('attributes').options[attributes.selectedIndex].attributes[1].textContent;
            let key = document.getElementById('attributes').options[attributes.selectedIndex].attributes[2].textContent;

            if (!attributes_added.includes(key)) {

                let form = document.getElementsByTagName('form')[0];

                if (!document.getElementById('add-button')) {

                    buttonDiv = document.createElement('div');
                    buttonDiv.classList.add('form-group');
                    buttonDiv.classList.add('row');
                    buttonDiv.innerHTML = ('<div class="col-sm-10"><button type="submit" id="add-button" class="btn btn-primary">Добави</button></div>');
                    form.appendChild(buttonDiv);

                }

                attributes_added.push(key);

                let button = document.getElementsByTagName('button')[0];
                let div = document.createElement('div');
                div.classList.add('form-group');
                div.classList.add('row');
                div.innerHTML = `<label for="${key}" class="col-sm-3 col-form-label">${value}</label>
                            <input type="text" id="${key}" name="${id}" class="form-control col-sm-8" placeholder="${value}">
                            <span id="close-button-${key}" class="btn btn-danger ml-2">X</span>`;
                button.parentNode.insertBefore(div, button);

                let span_button = document.getElementById(`close-button-${key}`);
                span_button.addEventListener('click', closeElement)

            }

        }

        function closeElement(e) {

            let key = e.target.id.split('-').slice(2).join('-');

            attributes_added = attributes_added.filter(function(value, index, arr){

                return value !== key;

            });

            e.target.parentElement.remove();
        }
    </script>