title: get start day of week and end day fullCalendar
body: <p>I´m traying to get actual week with <code>fullCalendar</code> plugin in <code>laravel 5.8</code>. I need get it, to send this date to controller and to do a query with this date.</p>
  <p>In my script.js i have a <code>listener click</code> but change my view to week and in this view in title put current week in this format:</p>
  <pre><code>8 – 14 mar 2021
  </code></pre>
  <p>i want to get firts day of week and last day of week. Also i´m traying with</p>
  <pre><code>var currentDate = calendar
  var beginOfWeek = currentDate.startOf('week');
  var endOfWeek = currentDate.endOf('week');
  </code></pre>
  <p>but returned me:</p>
  <pre><code>currentDate.startOf is not a function
  </code></pre>
  <p>because <code>currentData</code> return empty array... But i´m instaciate my calendar so:</p>
  <pre><code>var calendar = new FullCalendar.Calendar(document.getElementById('calendar'), {
      headerToolbar: {
          left: 'prev next today',
          center: 'title',
          right: 'dayGridDay dayGridWeek dayGridMonth listMonth'
      },
      locale: config.lang,
      initialView: 'dayGridMonth',
      displayEventTime: true,
      
      events: dbEvents,
  </code></pre>
  <p>and i have all my events from DB in my calendar... I don´t understand why i can´t use my object to use <code>startOf</code> and <code>endOf</code>.</p>
  <p>I don´t know i´m doing well my logic, maybe i should to do this to other form. How can i get current week? and even i want show next or last week that i can get this week ok.</p>
  <p>Thanks so much for help, and sorry for my english i hope that you can understand me.</p>