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Building Site Navigation with Markdown and Nokogiri

August 2, 2011

Who knew that Markdown — in my opinion the best text-to-HTML syntax available — could be used for something other than blog posts (or Github readme files)? Turns out that Markdown can be used as a powerful way to make web app navigation really simple to edit, even by non-developers. The task I set out to do was to turn something like this:

* Home
* About
    * About Us
    * API
    * Terms of Use
* Browse
* Etc.

into a nice dropdown menu. Making this markdown text available to a view is a fairly simple task. In Ruby on Rails, if you have a Page model that can hold Markdown text, you simply have to fetch it in the controller and call .to_html.html_safe on it. Also, with the help of some ternary operator elegance, you should make sure that if the page doesn’t exist, the code doesn’t blow up.

c_nav = Page.find_by_slug 'client-nav'
@client_nav = c_nav.nil? ? '' : c_nav.to_html.html_safe

So now, with the addition of a simple line in the view where we dump the contents of @client_nav onto the page, we’ve accomplished displaying a terrible looking unordered list when we could have just hard coded a nice looking menu in Haml. Here comes the fun part.

The obvious first choice for this task was to use jQuery to dynamically add CSS styles to the unordered list to turn it into a nice navigation menu. With the use of jQuery’s addClass method this is fairly simple, and it worked when I implemented it with just a couple lines of code. Unfortunately it resulted in annoying flickering as the page loaded because the unordered list is displayed un-styled for a split second (unacceptable). This could probably be fixed, but why bother doing something on the browser when it can be handled perfectly well on the server? After a couple of painful hours attempting to add classes to the generated HTML using Ruby string manipulation techniques and having little success, I discovered that this problem had already been solved by the creators of the Nokogiri gem.

To begin turning the raw HTML into styled goodness, I first stripped out the opening and closing ul tags manually. I enclosed the code to do this in a beginrescueend block because the test suite I’m using (Rspec) didn’t like me using negative numbers for indexes in a string for some reason.

   @client_nav[0..3] = ""
   @client_nav[-5..-1] = ""

Then I let Nokogiri work it’s magic.

@client_nav = Nokogiri::HTML::DocumentFragment.parse(@client_nav)
@client_nav.css("li:root").each do |anchor|
   anchor['class'] = 'nav_item'
@client_nav.css("li:has(ul)").each do |anchor|
   anchor['class'] = "nav_item more"
@client_nav.css("ul:first-child").each do |anchor|
   anchor['class'] = "dropdown"
@client_nav = @client_nav.to_html.html_safe

Because the HTML I was passing to Nokogiri is just a fragment of an unordered list, I used the DocumentFragment.parse method to prepare the HTML for Nokogiri to dynamically add CSS. Then, using basic CSS selectors (as well as one really useful one — has() — taken from jQuery), I added the proper classes to the list elements. It worked like a charm.

I’ll leave the CSS magic up to you — suffice it to say that with the proper stylesheets, this can look really great and is infinitely configurable. Why bother with bulky client-side code when Nokogiri provides a just as (perhaps even more) elegant solution?

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