JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <div>
    <input id="apartment" type="text">
    <div class="custom-placeholder">Кв./офис</div>
  </div>
  <div>
    <input id="floor" type="text">
    <div class="custom-placeholder">Этаж</div>
  </div>
  <div>
    <input id="entrance" type="text">
    <div class="custom-placeholder">Подъезд</div>
  </div>
  <div>
    <input id="intercom" type="text">
    <div class="custom-placeholder">Код домофона</div>
  </div>
</div>

CSS

.completed {color: blue; font-weight:bold;}

JavaScript

var $inputs = $('#floor, #entrance, #apartment, #intercom');
$inputs.on('blur', function(e) {
  if ($(this).val()) {
    $(this).next('.custom-placeholder').toggleClass('completed', true);
  } else {
    $(this).next('.custom-placeholder').removeClass('completed');
  }
  sessionStorage.setItem("PlaceholderCompleted", JSON.stringify($inputs.filter(function() {
    return !!$(this).val();
  }).map(function() {
    return $(this).attr("id");
  }).get()));
});

var stored = sessionStorage.getItem("PlaceholderCompleted");
stored = stored? JSON.parse(stored) : {};
for (var key in stored) {
  $("#" + stored[key]).siblings(".custom-placeholder").addClass('completed');
  console.log(key, stored[key]);
  console.log("#" + stored[key]);
}