Highlight link to current page

Often to improve your navigation UI (user experience), you will want to mark the link to current page “active”:

2023 Update

Use active_link_to instead of link_to to apply classes underline font-bold to links in your app.

# app/helpers/application_helper.rb
  def active_link_to(text = nil, path = nil, **options, &)
    link = block_given? ? text : path

    options[:class] = class_names(options[:class], 'underline font-bold') if current_page?(link)

    if block_given?
      link_to(link, options, &)
    else
      link_to text, path, options
    end
  end

class_names that we are using was introduced in Rails 6.1

active_link_to works with both inline link_to and block:

<%= active_link_to "Posts", posts_path %>

<%= active_link_to posts_path do %>
  Posts
<% end %>

Writing tests for active_link_to:

# test/helpers/application_helper_test.rb
class ApplicationHelperTest < ActionView::TestCase
  test 'active_link_to' do
    def current_page?(link)
      true
    end

    assert_equal(
      active_link_to('Home', static_pages_pricing_path),
      link_to('Home', static_pages_pricing_path, class: "active")
    )

    def current_page?(link)
      false
    end

    assert_equal(
      active_link_to('Home', static_pages_pricing_path),
      link_to('Home', static_pages_pricing_path)
    )
  end
end

Original approach:

The simple way to do it (assuming a bootstrap navbar):

<li class="<%= 'active fw-bold' if current_page?(root_path) %> nav-item">
  <%= link_to "Homepage", root_path, class: 'nav-link' %>   
</li>

or if you want to add some fancy fontawesome:

<li class="<%= 'active fw-bold' if current_page?(root_path) %> nav-item">
  <%= link_to root_path, class: 'nav-link' do %>
    <i class="fa fa-home"></i>
    Homepage
  <% end %>
</li>

however when you have a lot of links, your code will look “dirty”.

To make it look cleaner, you can add the following lines to application_helper.rb:

def active_link_to(name, path)
    content_tag(:li, class: "#{'active fw-bold' if current_page?(path)} nav-item") do
      link_to name, path, class: "nav-link"
    end
  end 
end 

def deep_active_link_to(path)
  content_tag(:li, class: "#{'active fw-bold' if current_page?(path)} nav-item") do
    link_to path, class: "nav-link" do
      yield
    end
  end 
end 

def deep_active_link_to_dropdown_item(path)
  content_tag(:li) do
    link_to path, class: "#{'active fw-bold' if current_page?(path)} dropdown-item" do
      yield
    end
  end 
end

this way you can write links like this

<%= active_link_to "homepage" root_path %>

or

<%= deep_active_link_to root_path do %>
  <i class="fa fa-home"></i>
  Homepage 
<% end %>