discourse/app/views/users/activate_account.html.erb

<div id='simple-container'>
    <h2><%= t 'activation.welcome_to', site_name: SiteSetting.title %></h2>
    <br/>
    <button class='btn' id='activate-account-button'><%= t 'activation.action' %></button>

    <%= form_tag(perform_activate_account_path, method: :put, id: 'activate-account-form') do %>
      <%= hidden_field_tag 'password_confirmation' %>
      <%= hidden_field_tag 'challenge' %>
    <% end %>
</div>

<%- content_for(:no_js_head) do %>
  <%= script "vendor" %>
<%- end %>

<script language="javascript">
  (function() {
    function activateAccount() {
      $('#activate-account-button').prop('disabled', true);
      $.ajax("/users/hp").then(function(hp) {
        $('#password_confirmation').val(hp.value);
        $('#challenge').val(hp.challenge.split("").reverse().join(""));
        $('#activate-account-form').submit();
      }).fail(function() {
        $('#activate-account-button').prop('disabled', false);
      });
    }

    var t0 = new Date().getTime();
    $('#activate-account-button').on('click', function() {
      var diff = new Date().getTime() - t0;

      // Ensure the form has been visible for a few ms before allowing the
      // user to submit.
      if (diff > 50) {
        activateAccount();
      }
    });
  })();
</script>