get the difference of days, excluded Saturday,Sunday and Holliday

I want to exclude the total of days but excluded saturday,sunday and holliday?? I dont know how? Im still trying to learn, my job is more on IT Technical, This is the first time I am trying to build a system with some help of googles.

Filing leave system.In this code,

I know this is from the idea of some templates in free source code, though as I said I am trying to learn :(

    <script>
        
        function calc_days(){
            var days = 0;
            if($('#date_start').val() != ''){
                var start = new Date($('#date_start').val());
                var end = new Date($('#date_end').val());
                var diffDate = (end - start) / (1000 * 60 * 60 * 24);
                days = Math.round(diffDate);
            }
            if($('#type').val() == 2)
                $('#leave_days').val('.5')
            else
                $('#leave_days').val(days +1)

        }
        $(document).ready(function(){
            $('.select2').select2();
            $('.select2-selection').addClass('form-control rounded-0')
            $('#type').change(function(){
                if($(this).val() == 2){
                console.log($(this).val())
                    $('#leave_days').val('.5')
                    $('#date_end').attr('required',false)
                    $('#date_end').val($('#date_start').val())
                    $('#date_end').closest('.form-group').hide('fast')
                }else{
                    $('#date_end').attr('reqiured',true)
                    $('#date_end').closest('.form-group').show('fast')
                    $('#leave_days').val(1)
                }
                calc_days()
            })
            $('#date_start, #date_end').change(function(){
                calc_days()
            })
            $('#leave_application-form').submit(function(e){
                e.preventDefault();
        </script>
    <?php
    <div class="form-group">
           <label for="type" class="control-label">Day Type</label>
                            <select id="type" name="type" class="form-control rounded-0">
                                <option value="1" <?php echo (isset($type) && $type ==1)?'selected' : '' ?>>Whole Day</option>
                                <option value="2" <?php echo (isset($type) && $type ==2)?'selected' : '' ?>>Half Day</option>
                            </select>
                        </div>
                        <div class="form-group">
                            <label for="date_start" class="control-label">Date Start</label>
                            <input type="date" id="date_start" class="form-control form" required name="date_start" value="<?php echo isset($date_start) ? date("Y-m-d",strtotime($date_start))  : '' ?>">
                            
                            
                        </div>
                        <div class="form-group">
                            <label for="date_end" class="control-label">Date End</label>
                            <input type="date" id="date_end" class="form-control form" required name="date_end" value="<?php echo isset($date_end) ? date("Y-m-d",strtotime($date_end)) : '' ?>">
                        </div>
                        <div class="form-group">
                            <label for="leave_days" class="control-label">Days</label>
                            <input type="number" id="leave_days" class="form-control form" name="leave_days" value="<?php echo isset($leave_days) ? $leave_days : 0 ?>" readonly>
                        </div>