Your code currently reinitialises the calendar every time you click a button. You should only initialise the calendar once, and then change the data it displays. To do that, you need to first remove the previous event source, add the new one, and then get the new events.
A suggestion: convention is that POST is for changing data (eg making a purchase, updating a record), while GET is for reading data. Here your event source is just loading event data to display, that really should be a GET request. Changing that also makes the code a bit simpler. I've changed to GET here, if you want to do this you need to change your PHP to respond to GET instead of POST.
Another suggestion: AFAICT you are using multiple non-unique HTML IDs on the same page. Your code suggests that the button is inside a loop, so you have buttons for multiple users, but your buttons all have the same ID:
<button id="cal" ...
The code you've shown does not use that ID, but if you try to, it won't work. IDs must be unique, if they are not and you try to use them, only the first one will work.
Another suggestion: it is generally considered best to separate your JS and your HTML, so instead of using inline onclick, use a separate event handler. You'll need to add the user ID to the button somehow, maybe with a data attribute:
<button data-id="' . $row["idutilizador"] . '" ...
And then instead of onclick() on that button, add an event handler in your JS:
$('button').on('click', function(e) {
// Prevent any default action the button click might normally
// do, eg submit a form or something.
e.preventDefault();
// Find the ID of the clicked button
var userID = $(this).data('id');
// Now call the calendar function with that ID
cale(userID);
});
The code below implementes all these suggestions.
UPDATE As per comments you're using FullCalendar v3, so here's a working v3 solution (click Run to see it in action). I've also converted the previous v5 solution into a working snippet, see below.
FullCalendar v3 solution
// The base URL where your events are. I'm using npoint JSON
// bins from https://www.npoint.io/, yours would be:
// var sourceURL = '../Components/calendar/load.php';
var sourceURL = 'https://api.npoint.io/';
// The current source (none initially)
var currentSource;
// The calendar
var calendar = $('#calendar').fullCalendar({
defaultDate: '2022-01-15',
editable:true,
header:{
left:'prev,next today',
center:'title',
right:'month,agendaWeek,agendaDay'
},
// no events initially
});
// Handle button clicks
$('button').on('click', function(e) {
// Prevent any default action the button click might normally
// do, eg submit a form or something.
e.preventDefault();
// Find the ID of the clicked button
var userID = $(this).data('id');
// Now call the calendar function with that ID
cale(userID);
});
// Update sources
function cale(uti) {
// First remove the current source. First time through
// there is no source, but that does not matter.
// v3: https://fullcalendar.io/docs/v3/removeEventSource
calendar.fullCalendar('removeEventSource', currentSource);
// Set up the URL to the new source. I'm using npoint JSON
// bins from https://www.npoint.io/, so this URL format is
// different to yours, you would use:
// currentSource = sourceURL + '?id=' + uti
currentSource = sourceURL + uti;
// Now add the new source. Note this will use a GET request
// to retrieve events. The new events will be immediately
// fetched and displayed.
// v3: https://fullcalendar.io/docs/v3/addEventSource
calendar.fullCalendar('addEventSource', currentSource);
}
hr {
margin: 20px 0;
}
<link href="https://cdnjs.cloudflare.com/ajax/libs/fullcalendar/3.4.0/fullcalendar.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fullcalendar/3.4.0/fullcalendar.min.js"></script>
Click to select a source:
<button data-id="965e830c3e8ab78990c5">Source 1</button>
<button data-id="5c8901e5173d5eab3ad6">Source 2</button>
<hr>
<div id="calendar"></div>
FullCalendar v5 solution
And here's the original v5 solution, as a working snippet, click Run to see it working.
// The base URL where your events are. I'm using npoint JSON
// bins from https://www.npoint.io/, yours would be:
// var sourceURL = '../Components/calendar/load.php';
var sourceURL = 'https://api.npoint.io/';
// The current source (none initially)
var currentSource;
// The calendar
var calendarEl = document.getElementById('calendar');
var calendar = new FullCalendar.Calendar(calendarEl, {
initialDate: '2022-01-15',
editable:true,
// no events initially
});
calendar.render();
// Handle button clicks
$('button').on('click', function(e) {
// Prevent any default action the button click might normally
// do, eg submit a form or something.
e.preventDefault();
// Find the ID of the clicked button
var userID = $(this).data('id');
// Now call the calendar function with that ID
cale(userID);
});
// Update sources
function cale(uti) {
// First get all the current event sources
// v5: https://fullcalendar.io/docs/Calendar-getEventSources
var sources = calendar.getEventSources();
// Now remove those event sources. Note the first time through there
// are none.
// v5: https://fullcalendar.io/docs/EventSource-remove
for (const source of sources) {
source.remove();
}
// Set up the URL to the new source. I'm using npoint JSON
// bins from https://www.npoint.io/, so this URL format is
// different to yours, you would use:
// currentSource = sourceURL + '?id=' + uti
currentSource = sourceURL + uti;
// Now add your new source. Note this will use a GET request to
// retrieve events. The new events will be immediately fetched
// and displayed.
// v5: https://fullcalendar.io/docs/Calendar-addEventSource
calendar.addEventSource(currentSource);
}
hr {
margin: 20px 0;
}
<link href="https://cdn.jsdelivr.net/npm/fullcalendar@5.10.1/main.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/fullcalendar@5.10.1/main.min.js"></script>
Click to select a source:
<button data-id="965e830c3e8ab78990c5">Source 1</button>
<button data-id="5c8901e5173d5eab3ad6">Source 2</button>
<hr>
<div id="calendar"></div>
