Dynamically adding a form to a Django formset with Ajax

This is how I do it, using jQuery:

My template:

<h3>My Services</h3>
{{ serviceFormset.management_form }}
{% for form in serviceFormset.forms %}
    <div class='table'>
    <table class='no_error'>
        {{ form.as_table }}
    </table>
    </div>
{% endfor %}
<input type="button" value="Add More" id="add_more">
<script>
    $('#add_more').click(function() {
        cloneMore('div.table:last', 'service');
    });
</script>

In a javascript file:

function cloneMore(selector, type) {
    var newElement = $(selector).clone(true);
    var total = $('#id_' + type + '-TOTAL_FORMS').val();
    newElement.find(':input').each(function() {
        var name = $(this).attr('name').replace('-' + (total-1) + '-','-' + total + '-');
        var id = 'id_' + name;
        $(this).attr({'name': name, 'id': id}).val('').removeAttr('checked');
    });
    newElement.find('label').each(function() {
        var newFor = $(this).attr('for').replace('-' + (total-1) + '-','-' + total + '-');
        $(this).attr('for', newFor);
    });
    total++;
    $('#id_' + type + '-TOTAL_FORMS').val(total);
    $(selector).after(newElement);
}

What it does:

cloneMore accepts selector as the first argument, and the type of formset as the 2nd one. What the selector should do is pass it what it should duplicate. In this case, I pass it div.table:last so that jQuery looks for the last table with a class of table. The :last part of it is important because the selector is also used to determine what the new form will be inserted after. More than likely you'd want it at the end of the rest of the forms. The type argument is so that we can update the management_form field, notably TOTAL_FORMS, as well as the actual form fields. If you have a formset full of, say, Client models, the management fields will have IDs of id_clients-TOTAL_FORMS and id_clients-INITIAL_FORMS, while the form fields will be in a format of id_clients-N-fieldname with N being the form number, starting with 0. So with the type argument the cloneMore function looks at how many forms there currently are, and goes through every input and label inside the new form replacing all the field names/ids from something like id_clients-(N)-name to id_clients-(N+1)-name and so on. After it is finished, it updates the TOTAL_FORMS field to reflect the new form and adds it to the end of the set.

This function is particularly helpful to me because the way it is setup it allows me to use it throughout the app when I want to provide more forms in a formset, and doesn't make me need to have a hidden "template" form to duplicate as long as I pass it the formset name and the format in which the forms are laid out. Hope it helps.

Simplified version of Paolo's answer using empty_form as a template.

<h3>My Services</h3>
{{ serviceFormset.management_form }}
<div id="form_set">
    {% for form in serviceFormset.forms %}
        <table class='no_error'>
            {{ form.as_table }}
        </table>
    {% endfor %}
</div>
<input type="button" value="Add More" id="add_more">
<div id="empty_form" style="display:none">
    <table class='no_error'>
        {{ serviceFormset.empty_form.as_table }}
    </table>
</div>
<script>
    $('#add_more').click(function() {
        var form_idx = $('#id_form-TOTAL_FORMS').val();
        $('#form_set').append($('#empty_form').html().replace(/__prefix__/g, form_idx));
        $('#id_form-TOTAL_FORMS').val(parseInt(form_idx) + 1);
    });
</script>

I've posted a snippet from an app I worked on a while back. Similar to Paolo's, but also allows you delete forms.