title: How to change a FullCalendar day cell via a js function call
body: <p>When I look at examples of changing the appearance or contents of a day cell in FullCalendar, they look like this:</p>
  <pre><code>    calendar: {
          height: 650,
          editable: true,
          header: {
              left: '',
              center: 'prev title next',
              right: ''
          },
          defaultView: 'month',
          dayRender: function (date, cell) {
                   $r = $scope.getDateInfo(date);
                  if($r){
                     cell.css(&quot;background-color&quot;, &quot;#ccf3ff&quot;); 
                  }
                  cell.html('&lt;i class=&quot;fa fa-line-chart&quot;  &gt;&lt;/i&gt;'+$r.amount+'&lt;br/&gt;&lt;i class=&quot;fa fa-user&quot; &gt;&lt;/i&gt;'+$r.users+'&lt;br/&gt;&lt;i class=&quot;fa fa-shopping-basket&quot; &gt;&lt;/i&gt;'+$r.income);
              }
  
      }
  };
  </code></pre>
  <p>But what I need to do differs than that context. I make an AJAX call to a PHP back end to return a list of holidays, like</p>
  <pre><code>0 =&gt; [
    '2022-05-30',
    'Memorial Day'
  ]
  </code></pre>
  <p>The called function doing the AJAX call gets passed a FullCalendar object. In the success section I have access to both the calendar object and the array of holidays.</p>
  <p>What I need to be able to do is get access to the cell for the holiday date and make changes to it... something akin to</p>
  <pre><code>let cell = calendar.dayRender('2022-05-30');
  cell.css(&quot;background-color&quot;, &quot;ccf3ff&quot;);
  cell.text(&quot;Memorial Day&quot;);
  </code></pre>
  <p>rather than looping through the entire calendar comparing the cell date to the desired date.</p>