Hide unselected form field in dropdown list in javascript

Question

I have a field with a drop down list in my html form. It contains two possibilities, I would like to make the following field (first block or second block) appear or disappear depending on the selection, I found for radio buttons but not for a drop-down list... Can you help me do this in javascript?

Thanks a lot.

Code html :

<div class="col-md-2">
        <select class="form-select text-secondary mt-4" id="autoSizingSelect" name="service">
          <option value="midi" data-id="#midi">Midi</option>
          <option value="soir" data-id="#soir">Soir</option>
        </select>
      </div>

// First block
<p class="text-secondary text-center mt-5">Heure midi</p>
      <div class="col-md-4">
        <select class="form-select text-secondary" id="midi" name="heure_midi">
          <option value=""></option>
          <option value=" 12:00">12:00</option>
          <option value="12:15">12:15</option>
          <option value="12:30">12:30</option>
          <option value="12:45">12:45</option>
          <option value="13:00">13:00</option>
          <option value="13:15">13:15</option>
          <option value="13:30">13:30</option>
          <option value="13:45">13:45</option>
          <option value="14:00">14:00</option>
        </select>
      </div>

//Second block         
<p class="text-secondary text-center mt-4">Heure soir</p>
      <div class="col-md-4">
        <select class="form-select text-secondary" id="soir" name="heure_soir">
          <option value=""></option>
          <option value="19:00">19:00</option>
          <option value="19:15">19:15</option>
          <option value="19:30">19:30</option>
          <option value="19:45">19:45</option>
          <option value="19:00">20:00</option>
          <option value="20:15">20:15</option>
          <option value="20:30">20:30</option>
          <option value="20:45">20:45</option>
          <option value="21:00">21:00</option>
        </select>
      </div>

Answer 1

You can combine document.querySelectorAll and classList.toggle triggered with the onchange event of the select to achieve this, with a predefined .hidden class.

Please see snippet exemple.

function handleChange(event){
  document.querySelectorAll('.container').forEach((form)=>{
    form.classList.toggle('hidden');
    
  })
}

.hidden {
  display: none;
}

<h1 id="header"></h1>
      <div class="col-md-2">
        <select class="form-select text-secondary mt-4" id="autoSizingSelect" name="service" onchange="handleChange(this)">
          <option value="midi" data-id="#midi">Midi</option>
          <option value="soir" data-id="#soir">Soir</option>
        </select>
      </div>


<div class="text-secondary text-center mt-5 container">
      <p class="col-md-4">
      <span>Heure midi</span>
        <select class="form-select text-secondary" id="midi" name="heure_midi">
          <option value=""></option>
          <option value="12:00">12:00</option>
          <option value="12:15">12:15</option>
          <option value="12:30">12:30</option>
          <option value="12:45">12:45</option>
          <option value="13:00">13:00</option>
          <option value="13:15">13:15</option>
          <option value="13:30">13:30</option>
          <option value="13:45">13:45</option>
          <option value="14:00">14:00</option>
        </select>
      </p>
</div>
        
<div class="text-secondary text-center mt-4 container hidden">
      <p class="col-md-4">
       <span>Heure soir</span>
        <select class="form-select text-secondary" id="soir" name="heure_soir">
          <option value=""></option>
          <option value="19:00">19:00</option>
          <option value="19:15">19:15</option>
          <option value="19:30">19:30</option>
          <option value="19:45">19:45</option>
          <option value="19:00">20:00</option>
          <option value="20:15">20:15</option>
          <option value="20:30">20:30</option>
          <option value="20:45">20:45</option>
          <option value="21:00">21:00</option>
        </select>
      </p>
    </div>