how to access javascript variable in rails view

You have to understand that ruby code in your views gets executed on the server - before any javascript on the page gets a change to be executed.

That's why you cannot do stuff like this:

<script>
  var js_var = 1;
</script>

<%= get_value_of_js_var_somehow %>

The other way round it works:

<script>
  var js_var = <% generate_value_with_ruby %>;
  do_something_in_javascript_with_js_var();
</script>

You can pass a javascript variable to rails using AJAX. For example if you want to pass the id for an user to a method in a rails controller from javascript you can execute the following code:

<script>
  var id = 1;
  <%= remote_function :url => {:controller=>'controller_name', :action=>'method_name'}, :with => "'user_id=' + id" %>
</script>

You will receive the variable through a POST request, as a parameter. You can access it using params[:user_id].

def method_name
  if params[:user_id].exists?
    u = User.where('id = ?', params[:user_id]).first
  end
  puts u.path
end

Hope I've answered your question.

If you have this Javascript variable in a higher piece of javascript (per se: the application.js), then you can always just reference it in the view.

#application.js
var someVar = "Hello World";

Then in your view (executed on the client), you could to...

<script type='text/javascript'>
  alert(someVar);
</script>

I think we need more specific ellaboration if one of these three posts doesn't answer your question.

Suppose we are having script as follows

<script type="text/javascript">
  var a="some value";
  document.getElementById('tagid').innerHTML='<%= tag(:div,content_tag(:p,' " +a+ " '), :id=>' " +a+ " ', name=>"somename") %>';
</script>