app/views/lessons/toggle_check.js.erb
<% if current_user.lessons.include?(@lesson) %>
$(<%= dom_id @lesson %>).html(
'<%= j link_to "Изменить статус на: \"Урок не завершен\"".html_safe, toggle_check_course_lesson_path(@course, @lesson), class: "mark-as-uncompleted", remote: true, method: :post %>'
);
$('#<%= dom_id @lesson %>').prepend("<div class=\"lesson_completed\"> \
<i class=\"fa fa-fw fa-check-square lesson_completed__icon\"></i> \
<div class=\"lesson_completed__text\">Урок Завершен</div> \
<div class=\"clear_b\"></div> \
</div>");
<% else %>
$(<%= dom_id @lesson %>).html(
'<%= j link_to "<i class=\"glyphicon glyphicon-unchecked\"></i>".html_safe, toggle_check_course_lesson_path(@course, @lesson), class: "mark-as-completed", remote: true, method: :post %>'
);
<% end %>