Rails active_link_to helper

application_helper.rb

module ApplicationHelper
  def active_class(link_path)
    current_path = request.path

    # Special case for root path
    return 'active' if current_path == '/' && link_path == '^/$'
    return '' if current_path != '/' && link_path == '^/$'

    # Use Regex to match the route or any conditions you need
    current_path.match(Regexp.new(link_path)) ? 'active' : ''
  end
end

usage.erb

<!-- app/views/layouts/application.html.erb -->
<nav>
  <ul>
    <li class="<%= active_class('^/$') %>">
      <%= link_to 'Home', root_path %>
    </li>
    <li class="<%= active_class('^/about') %>">
      <%= link_to 'About', about_path %>
    </li>
    <li class="<%= active_class('^/contact') %>">
      <%= link_to 'Contact', contact_path %>
    </li>
  </ul>
</nav>