mamweb/seminar/static/seminar/dynamic_formsets.js

// Credit https://medium.com/all-about-django/adding-forms-dynamically-to-a-django-formset-375f1090c2b0
function updateElementIndex(el, prefix, ndx) {
	var id_regex = new RegExp('(' + prefix + '-\\d+)');
	var replacement = prefix + '-' + ndx;
	if ($(el).attr("for")) {
		$(el).attr("for", $(el).attr("for").replace(id_regex, replacement));
	}
	if (el.id) {
		el.id = el.id.replace(id_regex, replacement);
	}
	if (el.name) {
		el.name = el.name.replace(id_regex, replacement);
	}
}

// Credit https://medium.com/all-about-django/adding-forms-dynamically-to-a-django-formset-375f1090c2b0
function deleteForm(prefix, btn) {
    var total = parseInt($('#id_' + prefix + '-TOTAL_FORMS').val());
    if (total >= 1){
        btn.closest('div').remove();
        var forms = $('.attachment');
        $('#id_' + prefix + '-TOTAL_FORMS').val(forms.length);
        for (var i=0, formCount=forms.length; i<formCount; i++) {
            $(forms.get(i)).find(':input').each(function() {
                updateElementIndex(this, prefix, i);
            });
        }
    }
    return false;
}

// Credit: https://simpleit.rocks/python/django/dynamic-add-form-with-add-button-in-django-modelformset-template/
$(document).ready(function(){
	$('#add_attachment').click(function() {
		var form_idx = $('#id_prilohy-TOTAL_FORMS').val();
		var new_form = $('#empty_form').html().replace(/__prefix__/g, form_idx);
		$('#form_set').append(new_form);
		// Newly created form has not the binding between remove button and remove function
		// We need to add it manually
		$('.remove_attachment').click(function(){
			deleteForm("prilohy",this);
		});
		$('#id_prilohy-TOTAL_FORMS').val(parseInt(form_idx) + 1);
	});
	$('.remove_attachment').click(function(){
		deleteForm("prilohy",this);
	});
});