add many.js

 $('form a.add_child').click(function() {
    // The link that was clicked on has a data-association attribute that points it to the correct ID to clone.
    var association = $(this).attr('data-association');
    // Grab the template of the fields you want to copy, convert it to a string via the html() method
    var template = $('#' + association + '_fields_template').html();
    // Create a random number to replace the ID / name
    var regexp = new RegExp('new_' + association, 'g');
    var new_id = new Date().getTime();
    // Replace and Insert
    $(this).parent().before(template.replace(regexp, new_id));
    return false;
  });