application.js

$(document).ready(function () {
  $('form').submit('click', function(event){
    
    event.preventDefault();

    var number = 1 + Math.floor(Math.random() * 6);
    var num = {"value" : number};
    var action = $(this).attr('action');
    

    $.post(action, num, function(response){
      $('#die').html(response)
    });
     
  });
  // PSEUDO-CODE:
  //   1- intercept the form submission event using jQuery
  //   2- prevent the default action for that event from happening
  //   3- generate a random number between 1 and 6 using JavaScript
  //   4- use jQuery to submit an AJAX post to the form's action
  //   5- when the AJAX post is done, replace the contents of the "#die" DIV in the DOM using jQuery

});

index.erb

<div class="container">
  <h1>Simplest Possible AJAX</h1>
  <p>This contrived app will simulate a roll of a 6-sided die.</p>

  <form method="post" action="/rolls">
    <input type="submit" value="Roll the Die">
  </form>

  <div id="die">
  </div>

</div>

index.rb

get '/' do
  erb :index
end


# TODO: convert this route to use AJAX
post '/rolls' do
  # If the user passes-in a "value", let's use it. Otherwise, we'll generate a random one.
  # See: roll_if_value_is_nil method in the Roll model.
  value = params[:value] ? params[:value].to_i : nil

  @roll = value ? Roll.create({ value: value }) : Roll.create

  erb :roll, layout: false  # HINT: what does this do? what should we do instead?
end

roll.erb

<img src="/<%= @roll.value %>.png" title="<%= @roll.value %>" alt="the roll">