What is the way to restrict some specific days of the week in input type=date?

Question

The main problem is that I can select Monday to Sunday, but I want to limit Tuesday, Thursday, Saturday, and Sunday to only select Monday, Wednesday, and Friday Here is the code I tried, but I don't actually know why it doesn't work:

Thanks! ! ! !

<form action="insertar_reserva_tarde.php" method="POST">
    <label for="fecReserva">Día:</label>
    <input type="date" name="fecReserva" id="fecReserva" min="2023-06-15" max="2023-07-15"required>
    <br>
    <label for="horIniReserva">Hora de inicio:</label>
    <select name="horIniReserva" id="horIniReserva">
        <option value="17">17:00</option>
        <option value="18">18:00</option>
        <option value="19">19:00</option>
        <option value="20">20:00</option>
    </select>
    <br>
    <label for="horFinReserva">Hora de fin:</label>
    <select name="horFinReserva" id="horFinReserva">
        <option value="18">18:00</option>
        <option value="19">19:00</option>
        <option value="20">20:00</option>
        <option value="21">21:00</option>
    </select>
    <br>
    <input type="hidden" name="pista" value="1">
    <input type="hidden" name="idHorario" value="1">
    <input type="submit" value="Reservar">
</form>
<?php
        if(isset($_POST['fecReserva'])){
            $date = strtotime($_POST['fecReserva']);
            $dayOfWeek = date('N', $date); // obtiene el número del día de la semana (1 = lunes, 2 = martes, etc.)
            if($dayOfWeek == 1 || $dayOfWeek == 3 || $dayOfWeek == 5){
                echo "<p>La fecha seleccionada es el ".date('d/m/Y', $date)."</p>";
            } else {
                echo "<p>Sólo se permiten reservas en Lunes, Miércoles y Viernes.</p>";
            }
        }
    ?>
    <script>// Everything except weekend days
        const validate = dateString => {
        const day = (new Date(dateString)).getDay();
        if (day==2 || day==4 || day==6 || day==0 ) {
            return false;
        }
        return true;
        }

        // Sets the value to '' in case of an invalid date
        document.querySelector('input').onchange = evt => {
        if (!validate(evt.target.value)) {
            evt.target.value = '';
        }
        }
    </script>

The purpose is to select only Monday, Wednesday and Friday

Answer 1

Your problem appears to be that you are attaching a listener to the input's change event and then returning false to that event.

If you only want to select odd days (based on ECMAScript day numbers), the function simply returns the result of !!(dayNum % 2).

The value of the input type date is a timestamp in the format YYYY-MM-DD, which will be parsed as UTC, so if you use new Date(value) you need to get the UTC date.

The logic is illustrated below by displaying a message that intentionally cancels form submission to display success and failure without submission.

There are many other ways to achieve the same result, for example you can use valueAsDate instead of calling the Date constructor. You can also use an array of allowed or not allowed dates and test it, etc.

window.onload = () => {

  // Related elements
  let form = document.getElementById('calendar');
  let msg = document.getElementById('msg');
  
  // The listener
  let checkDate = evt => {
  
    // Cancel submit if called from submit
    if (evt.type == 'submit') evt.preventDefault();
    
    // Value parsed as UTC so get UTC day
    let day = new Date(form.theDate.value).getUTCDay();
    // Check if day is valid
    let isValid = !!(day % 2);
    
    // Do stuff based on whether isValid is true or false
    // Show message based on selected day
    let days = ['Sunday','Monday','Tuesday','Wednesay','Thursday','Friday','Saturday']
    msg.textContent = `Selected day is ${days[day]}, ` +
      `${isValid? 'pass.' : 'fail. Must be a Monday, Wednesday or Friday'}`;
      
    return isValid;
  }
  
  // Attach listeners - deal with form being submitted without setting a date
  form.addEventListener('change', checkDate);
  form.addEventListener('submit', checkDate);
}

#msg {
  color: #999999;
  font-family: sans-serif;
}

<form id="calendar" onsubmit="return false">
  <label for="theDate">Date:</label>
  <input type="date" id="theDate" name="theDate">
  <span id="msg"></span><br>
  <button>Submit</button>
</form>