Called and canceled of the admin-ajax.php file multiple times - php

Question

I have an issue in a Wordpress installation with a plugin. There is a calendar which you can click on a day (or a range of days) and from ajax calls through admin-ajax.php it calculates product costs.
The problem is that, when I click on a calendar cell, the admin-ajax.php is called twice. The first time for a few milliseconds and canceled immediately. Then automatically, it calls it once again and get the ajax response. When I click for a second time on a calendar cell, the admin-ajax.php is called 3 times. The first two are canceled and only the last one get a response.
I found that the code that is used for this part is the following. However, I cannot find any issue on it, even if I can see those cancelled calls on Developer console.
$('.wc-bookings-booking-form')
.on('change', 'input, select', function() {
var index = $('.wc-bookings-booking-form').index(this);
if ( xhr[index] ) {
xhr[index].abort();
}
$form = $(this).closest('form');
var required_fields = $form.find('input.required_for_calculation');
var filled = true;
$.each( required_fields, function( index, field ) {
var value = $(field).val();
if ( ! value ) {
filled = false;
}
});
if ( ! filled ) {
$form.find('.wc-bookings-booking-cost').hide();
return;
}
$form.find('.wc-bookings-booking-cost').block({message: null, overlayCSS: {background: '#fff', backgroundSize: '16px 16px', opacity: 0.6}}).show();
xhr[index] = $.ajax({
type: 'POST',
url: booking_form_params.ajax_url,
data: {
action: 'wc_bookings_calculate_costs',
form: $form.serialize()
},
success: function( code ) {
if ( code.charAt(0) !== '{' ) {
console.log( code );
code = '{' + code.split(/\{(.+)?/)[1];
}
result = $.parseJSON( code );
if ( result.result == 'ERROR' ) {
$form.find('.wc-bookings-booking-cost').html( result.html );
$form.find('.wc-bookings-booking-cost').unblock();
$form.find('.single_add_to_cart_button').addClass('disabled');
} else if ( result.result == 'SUCCESS' ) {
$form.find('.wc-bookings-booking-cost').html( result.html );
$form.find('.wc-bookings-booking-cost').unblock();
$form.find('.single_add_to_cart_button').removeClass('disabled');
} else {
$form.find('.wc-bookings-booking-cost').hide();
$form.find('.single_add_to_cart_button').addClass('disabled');
console.log( code );
}
},
error: function() {
$form.find('.wc-bookings-booking-cost').hide();
$form.find('.single_add_to_cart_button').addClass('disabled');
},
dataType: "html"
});
})
.each(function(){
var button = $(this).closest('form').find('.single_add_to_cart_button');
button.addClass('disabled');
});
And here is a screenshot from the Dev Console:
EDIT: I think I found the problem, but I am not sure. There is also this part of code which was supposed to not used at all. There is a feature for time on calendar, but it isn't activated. So, this code should not be run.
$('.wc-bookings-booking-form').on( 'date-selected', function() {
show_available_time_blocks( this );
});
var xhr;
function show_available_time_blocks( element ) {
var $form = $(element).closest('form');
var block_picker = $form.find('.block-picker');
var fieldset = $form.find('.wc_bookings_field_start_date');
var year = parseInt( fieldset.find( 'input.booking_date_year' ).val(), 10 );
var month = parseInt( fieldset.find( 'input.booking_date_month' ).val(), 10 );
var day = parseInt( fieldset.find( 'input.booking_date_day' ).val(), 10 );
if ( ! year || ! month || ! day ) {
return;
}
// clear blocks
block_picker.closest('div').find('input').val( '' ).change();
block_picker.closest('div').block({message: null, overlayCSS: {background: '#fff', backgroundSize: '16px 16px', opacity: 0.6}}).show();
// Get blocks via ajax
if ( xhr ) xhr.abort();
xhr = $.ajax({
type: 'POST',
url: booking_form_params.ajax_url,
data: {
action: 'wc_bookings_get_blocks',
form: $form.serialize()
},
success: function( code ) {
block_picker.html( code );
resize_blocks();
block_picker.closest('div').unblock();
},
dataType: "html"
});
}