Bootstrap 5 select dropdown with multiple value display properties

I have the following code<hr> HTML

<select id="select" placeholder="Choose Select" class="selectpicker" multiple></select>
<div class="container">
    <div id="all" class="items">ALL</div>
    <div id="1" class="items">Div_1</div>
    <div id="2" class="items">Div_2</div>
    <div id="3" class="items">Div_3</div>
    <div id="4" class="items">Div_4</div>
    <div id="5" class="items">Div_5</div>
    <div id="6" class="items">Div_6</div>
</div>

Javascript <hr>

var select = document.getElementById('select');
var elems = document.querySelectorAll('.items');

var obj = {};
var filtered = [].filter.call(elems, function (el) {
    if (!obj[el.id]) {
        obj[el.id] = true;
        return true;
    } else {
        return false;
    }
});
var selectOpt = filtered.map(function (el) {
    el.style.display = 'block';
    return `<option> ${el.id} </option>`;
});
select.innerHTML = selectOpt.join('');
select.addEventListener('change', function () {
    for (var i = 0, iLen = select.options.length; i < iLen; i++) {
        var opt = select.options[i];
        var val = opt.value || opt.text;
        if (opt.selected) {
            document.getElementById(val).style.display = 'block';
        } else {
            document.getElementById(val).style.display = 'none';
        }

    }
});

How can I add show all property when nothing is selected or I choose show all. Thank you!

I tried adding the condition and it didn't work. Please who can help me Thank You!

A quick and simple solution is to check the text of opt for all and then get all items and set the display style to block.

Disclaimer: Nested ifs are pretty ugly and not best practice. So feel free to refacor. :D

  if (opt.innerText === 'all') {
    var items = document.getElementsByClassName('items');
    for (i = 0; i < items.length; i++) {
      items[i].style.display = 'block';
    }
    return;
  }

var select = document.getElementById('select');
var elems = document.querySelectorAll('.items');

var obj = {};
var filtered = [].filter.call(elems, function(el) {
  if (!obj[el.id]) {
    obj[el.id] = true;
    return true;
  } else {
    return false;
  }
});
var selectOpt = filtered.map(function(el) {
  el.style.display = 'block';
  return `<option> ${el.id} </option>`;
});
select.innerHTML = selectOpt.join('');
select.addEventListener('change', function() {
  for (var i = 0, iLen = select.options.length; i < iLen; i++) {
    var opt = select.options[i];

    var val = opt.value || opt.text;
    if (opt.selected) {
      if (opt.innerText === 'all') {
        var items = document.getElementsByClassName('items');
        for (i = 0; i < items.length; i++) {
          items[i].style.display = 'block';
        }
        return;
      }
      document.getElementById(val).style.display = 'block';
    } else {
      document.getElementById(val).style.display = 'none';
    }

  }
});

<select id="select" placeholder="Choose Select" class="selectpicker" multiple></select>
<div class="container">
  <div id="all" class="items">ALL</div>
  <div id="1" class="items">Div_1</div>
  <div id="2" class="items">Div_2</div>
  <div id="3" class="items">Div_3</div>
  <div id="4" class="items">Div_4</div>
  <div id="5" class="items">Div_5</div>
  <div id="6" class="items">Div_6</div>
</div>