ActionController::UnknownFormat when add resond_to

When I remove respond_to and render to view, everything works fine but adding the js render gives an error.

controller code :

if params[:stock].present?
  @data = params[:stock]
  @stock = Stock.new_form_lookup(params[:stock])
  respond_to do | format |
      format.js  {render partial: 'user/result'} 
  end
else
  flash[:danger] = "no search found "
  redirect_to my_portfolio_path
end

end

View code:

<%= form_tag searchstock_path , remote: true , method: :get, id:"stock-search" do %>

application.js code:

//= rails-ujs
//= require jquery
//= require bootstrap
//= require jquery_ujs
//= require turbolinks
//= require_tree .

from ActionController::UnknownFormat when add resond_to