jquery - bootstrap datepicker rails gem is not working -

i don't understand why datepicker gem not working. here code of app:

here gemfile:

source 'https://rubygems.org'  git_source(:github) |repo_name|   repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")   "https://github.com/#{repo_name}.git" end   # bundle edge rails instead: gem 'rails', github: 'rails/rails' gem 'rails', '~> 5.1.3' # use sqlite3 database active record gem 'devise' gem 'milia', github: 'jekuno/milia', ref: '05b72dd' gem 'aws-sdk' gem 'stripe' # use puma app server gem 'puma', '~> 3.7' # use scss stylesheets gem 'sass-rails', '~> 5.0' # use uglifier compressor javascript assets gem 'uglifier', '>= 1.3.0' # see https://github.com/rails/execjs#readme more supported runtimes # gem 'therubyracer', platforms: :ruby  # use coffeescript .coffee assets , views gem 'coffee-rails', '~> 4.2' # turbolinks makes navigating web application faster. read more: https://github.com/turbolinks/turbolinks gem 'turbolinks', '~> 5' # build json apis ease. read more: https://github.com/rails/jbuilder gem 'jbuilder', '~> 2.5' gem 'jquery-rails' gem 'twitter-bootstrap-rails' gem 'devise-bootstrap-views' gem 'bootstrap-datepicker-rails'  gem 'certified' # use redis adapter run action cable in production # gem 'redis', '~> 3.0' # use activemodel has_secure_password # gem 'bcrypt', '~> 3.1.7'  # use capistrano deployment # gem 'capistrano-rails', group: :development  group :development, :test   gem 'sqlite3'   # call 'byebug' anywhere in code stop execution , debugger console   gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]   # adds support capybara system testing , selenium driver   gem 'capybara', '~> 2.13'   gem 'selenium-webdriver' end  group :development   # access irb console on exception pages or using <%= console %> anywhere in code.   gem 'web-console', '>= 3.3.0' end  # windows not include zoneinfo files, bundle tzinfo-data gem gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]  gem 'activerecord-session_store', github: 'rails/activerecord-session_store' 

here application.css file:

/*  * manifest file that'll compiled application.css, include files  * listed below.  *  * css , scss file within directory, lib/assets/stylesheets, or plugin's  * vendor/assets/stylesheets directory can referenced here using relative path.  *  * you're free add application-wide styles file , they'll appear @ bottom of  * compiled file styles add here take precedence on styles defined in other css/scss  * files in directory. styles in file should added after last require_* statement.  * better create new file per style scope.  *  *= require devise_bootstrap_views  *= require bootstrap-datepicker3  *= require_tree .  *= require_self  */ 

here application.js file:

// manifest file that'll compiled application.js, include files // listed below. // // javascript/coffee file within directory, lib/assets/javascripts, or plugin's // vendor/assets/javascripts directory can referenced here using relative path. // // it's not advisable add code directly here, if do, it'll appear @ bottom of // compiled file. javascript code in file should added after last require_* statement. // // read sprockets readme (https://github.com/rails/sprockets#sprockets-directives) details // supported directives. // //= require rails-ujs //= require jquery //= require jquery_ujs //= require twitter/bootstrap //= require bootstrap-datepicker //= require turbolinks //= require_tree . 

here datepicker.js file:

$(document).ready(function(){      $(function() {          $('.datepicker').datepicker({format: 'yyyy-mm-dd'});      });  }); 

here snippet of _form.html.erb file:

</div>   <div class="form-group">     <%= f.label :expected_completion_date, :class => 'control-label col-lg-2' %>     <div class="col-lg-10">       <%= f.text_field :expected_completion_date, :class => 'form-control datepicker' %>     </div> 

i did everything, don't know why datepicker gem not working.. there mistake made there.. if plz correct me , help..