Problems keeping an object in an array, Ruby issues and Rails issues

I'm trying to add an object to my array, however the array seems to always reset, instead of adding. What am I doing wrong? I think it has to do with if(defined? libraryshelf) then, What I'm trying to do here is find out of the array exists or not (if this is the first add or not)..

def add_book
  @listofbooks ||= Array.new
  @listofbooks.push(params[:booktitle])
  @listofbooks
  respond_to do |format|
    format.html { redirect_to(:back) }
    format.js
  end
end

my add_book.js.erb file

alert('<%= @listofbooks %>');

@listofbooks only shows the title of the book I last added..