How to check if variable is undefined

I am using HAML and jquery to code my application. I have a single 'Share' template that is used to display a URL link. I want it to be flexible such that it will display different URLs depending on the variables that are passed into it.

//Code to trigger view and populate template -> Note I only pass in the thread vara here
 share_view = new Onethingaday.Views.Threads.ShareView
   thread: new Onethingaday.Models.Thread(@options.thread_muses.first().get('question'))
 
 //snippet from share view to pass the variables to the template
 render: ->
   $(@el).html @template
     nickname: @options.nickname
     thread_slug: @options.thread.get('slug')
     thread_text: @options.thread.get('text')
   @
 
 //Snippet of share view's template. Added if-else statement to check if nickname is defined
 .sidebar_text Link:
   <% if (typeof <%= nickname %> !== "undefined") { %>
   %input.detail_text{value: "<%= 'http://dailymus.es/' + nickname + '/threads/' + thread_slug %>"}
   <% } else { %>
   %input.detail_text{value: "<%= 'http://dailymus.es/' + '/threads/' + thread_slug %>"}
   <% } %>
 

In the above example, I did not define "nickname" variable. I expect that the else portion will be triggered and the URL displayed is "http://dailymus.es/threads/some-slug-text"

However I am still getting the following

As you see, it is still triggering the 'if' portion and displaying the 'undefined' as part of the URL.

How can I correctly check for 'undefined' variables in my case?

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