flask/examples/javascript/js_example/templates/jquery.html

{% extends 'base.html' %}

{% block intro %}
  <a href="https://jquery.com/">jQuery</a> is a popular library that
  adds cross browser APIs for common tasks. However, it requires loading
  an extra library.
{% endblock %}

{% block script %}
  <script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
  <script>
    function addSubmit(ev) {
      ev.preventDefault();
      $.ajax({
        method: 'POST',
        url: {{ url_for('add')|tojson }},
        data: $(this).serialize()
      }).done(addShow);
    }

    function addShow(data) {
      $('#result').text(data.result);
    }

    $('#calc').on('submit', addSubmit);
  </script>
{% endblock %}