Change image opacity when selecting option from form

Question

How can I change the opacity of the image for id Master to 1 when I select the option with value 1 (MasterCard)? and put it into a function that works on those 4 values, each with its own id? I want the default image to be 0.3 and when one of the options is selected the image has an opacity of 1.

.itemForm2 {
  width: 100%;
  position: relative;
  margin-bottom: 18px;
  margin-top: 10px;
  display: flex;
  flex-direction: row;
}

.escolhaCartao {
  display: flex;
  flex-direction: row;
  width: 218px!important;
  gap: 10px;
}

@media(min-width:768px) {
  .escolhaCartao {
    width: 258px!important;
    height: 34.32px;
    gap: 5px;
  }
  .lineFormCartao {
    display: flex;
    flex-direction: row;
    justify-content: inherit;
    gap: 16px;
  }
  .escolhaCartao img {
    opacity: .3;
  }
}

<div class="lineForm lineFormCartao">
  <div class="itemForm">
    <select id="OpcoesCartao" name="OpcoesCartao">
      <option value="1">Mastercard</option>
      <option value="2">Visa</option>
      <option value="3">Elo</option>
      <option value="4">Amex</option>
    </select>
  </div>
  <div class="itemForm2 escolhaCartao">
    <img id="master" src="images/master.png" alt="Logo cartão Mastercard">
    <img id="visa" src="images/visa.png" alt="Logo cartão Visa">
    <img id="elo" src="images/elo.png" alt="Logo cartão Elo">
    <img id="amex" src="images/amex.png" alt="Logo cartão Amex">
  </div>
</div>

Answer 1

Only using CSS and has

.escolhaCartao img {
 opacity: .2;
}

.itemForm:has(option[value="1"]:checked) + .itemForm2 > #master,
.itemForm:has(option[value="2"]:checked) + .itemForm2 > #visa,
.itemForm:has(option[value="3"]:checked) + .itemForm2 > #elo,
.itemForm:has(option[value="4"]:checked) + .itemForm2 > #amex
{
  opacity: 1;
}

  

    
      Mastercard
      Visa
      Elo
      Amex
    
  
  

    
    
    
    
  

Using JavaScript

var sel = document.querySelector("#OpcoesCartao");
const imgs =  document.querySelectorAll(".escolhaCartao img");

sel.addEventListener("change", function (e) {
  const val = this.value;
  const selected = document.querySelector(".escolhaCartao img.selected");
  if (selected) {
    selected.classList.remove('selected');
  }
  imgs[+val - 1].classList.add('selected');
});

sel.dispatchEvent(new Event('change'));

.escolhaCartao img {
 opacity: .2;
}

.escolhaCartao img.selected
{
  opacity: 1;
}

  

    
      Mastercard
      Visa
      Elo
      Amex
    
  
  

    
    
    
    
  

Answer 2

You can do this. This works in most browsers. Firefox should support it soon (https://caniuse.com/?search=has)

.itemForm2 {
    width: 100%;
    position: relative;
    margin-bottom: 18px;
    margin-top: 10px;
    display: flex;
    flex-direction: row;
}

.escolhaCartao {
    display: flex;
    flex-direction: row;
    width: 218px!important;
    gap: 10px;
}

.lineForm:has( option[value="1"]:checked ) #master {
  opacity: 1;
}
.lineForm:has( option[value="2"]:checked ) #visa {
  opacity: 1;
}
.lineForm:has( option[value="3"]:checked ) #elo {
  opacity: 1;
}
.lineForm:has( option[value="4"]:checked ) #amex {
  opacity: 1;
}


    .escolhaCartao {
        width: 258px!important;
        height: 34.32px;
        gap: 5px;
    }

    .lineFormCartao {
        display: flex;
        flex-direction: row;
        justify-content: inherit;
        gap: 16px;
    }
    .escolhaCartao img {
        opacity: .3;
    }

        

             
                 Mastercard
                 Visa
                 Elo
                 Amex