Reading session array from an external javascript file

Hello,

In my MVC application I have a function to read the column names and store it in a session array. Below is the code which I used.

 public void SetViewBag(int id)
        {
            try
            {
                connection();
                SqlCommand cmd = new SqlCommand("obps_sp_getColDetails", con);
                cmd.CommandType = CommandType.StoredProcedure;

                con.Open();
                SqlDataReader rdr = cmd.ExecuteReader();
                List colname = new List(250);

                while (rdr.Read())
                {
                    colname.Add(rdr[0].ToString());
                }
                Session["colname"] = colname;
            }
            finally
            {
                con.Close();
                con.Dispose();
            }

        }

 This session values are accessed from a view page using the code which shown in the image attached.

Now I want to remove this from the view page and add this function in a seperate javascript file. 
But when I used the function Test same like this in the js file, it is throughing error. 
Can some please help me to find a way to read the session array inside a javascript file.