Given Button into a Dropdown

Question

To Utilize web-space effectively i need to change the look of button to drop down list fashion:

HTML:

<h2>Filter DIV Elements</h2>

<div id="myBtnContainer">
  <button class="btn active" onclick="filterSelection('all')"> Show all</button>
  <button class="btn" onclick="filterSelection('cars')"> Cars</button>
  <button class="btn" onclick="filterSelection('animals')"> Animals</button>
  <button class="btn" onclick="filterSelection('fruits')"> Fruits</button>
  <button class="btn" onclick="filterSelection('colors')"> Colors</button>
</div>

<div class="container">
  <div class="filterDiv cars">BMW</div>
  <div class="filterDiv colors fruits">Orange</div>
  <div class="filterDiv cars">Volvo</div>
  <div class="filterDiv colors">Red</div>
  <div class="filterDiv cars animals">Mustang</div>
  <div class="filterDiv colors">Blue</div>
  <div class="filterDiv animals">Cat</div>
  <div class="filterDiv animals">Dog</div>
  <div class="filterDiv fruits">Melon</div>
  <div class="filterDiv fruits animals">Kiwi</div>
  <div class="filterDiv fruits">Banana</div>
  <div class="filterDiv fruits">Lemon</div>
  <div class="filterDiv animals">Cow</div>
</div>

CSS:

.filterDiv {
  float: left;
  background-color: #2196F3;
  color: #ffffff;
  width: 100px;
  line-height: 100px;
  text-align: center;
  margin: 2px;
  display: none;
}

.show {
  display: block;
}

.container {
  margin-top: 20px;
  overflow: hidden;
}

/* Style the buttons */
.btn {
  border: none;
  outline: none;
  padding: 12px 16px;
  background-color: #f1f1f1;
  cursor: pointer;
}

.btn:hover {
  background-color: #ddd;
}

.btn.active {
  background-color: #666;
  color: white;
}

JS:

    filterSelection("all")
function filterSelection(c) {
  var x, i;
  x = document.getElementsByClassName("filterDiv");
  if (c == "all") c = "";
  for (i = 0; i < x.length; i++) {
    w3RemoveClass(x[i], "show");
    if (x[i].className.indexOf(c) > -1) w3AddClass(x[i], "show");
  }
}

function w3AddClass(element, name) {
  var i, arr1, arr2;
  arr1 = element.className.split(" ");
  arr2 = name.split(" ");
  for (i = 0; i < arr2.length; i++) {
    if (arr1.indexOf(arr2[i]) == -1) {element.className += " " + arr2[i];}
  }
}

function w3RemoveClass(element, name) {
  var i, arr1, arr2;
  arr1 = element.className.split(" ");
  arr2 = name.split(" ");
  for (i = 0; i < arr2.length; i++) {
    while (arr1.indexOf(arr2[i]) > -1) {
      arr1.splice(arr1.indexOf(arr2[i]), 1);     
    }
  }
  element.className = arr1.join(" ");
}

// Add active class to the current button (highlight it)
var btnContainer = document.getElementById("myBtnContainer");
var btns = btnContainer.getElementsByClassName("btn");
for (var i = 0; i < btns.length; i++) {
  btns[i].addEventListener("click", function(){
    var current = document.getElementsByClassName("active");
    current[0].className = current[0].className.replace(" active", "");
    this.className += " active";
  });
}

Codepen link

Answer 1

you can just change the click event handler to onchange and replace all you div elements with <select> form input, I think here is what you are looking for, also a codepen:

// filterSelection("all")
var event = new Event('change');

// Dispatch onchange event here.
document.getElementById('myBtnContainer').dispatchEvent(event);

function handleChange(event) {
  let c = event.target.value;
  var x, i;
  x = document.getElementsByClassName("filterDiv");
  if (c == "all") c = "";
  for (i = 0; i < x.length; i++) {
    w3RemoveClass(x[i], "show");
    if (x[i].className.indexOf(c) > -1) w3AddClass(x[i], "show");
  }
}

function w3AddClass(element, name) {
  var i, arr1, arr2;
  arr1 = element.className.split(" ");
  arr2 = name.split(" ");
  for (i = 0; i < arr2.length; i++) {
    if (arr1.indexOf(arr2[i]) == -1) {element.className += " " + arr2[i];}
  }
}

function w3RemoveClass(element, name) {
  var i, arr1, arr2;
  arr1 = element.className.split(" ");
  arr2 = name.split(" ");
  for (i = 0; i < arr2.length; i++) {
    while (arr1.indexOf(arr2[i]) > -1) {
      arr1.splice(arr1.indexOf(arr2[i]), 1);     
    }
  }
  element.className = arr1.join(" ");
}

// Add active class to the current button (highlight it)
var btnContainer = document.getElementById("myBtnContainer");
var btns = btnContainer.getElementsByClassName("btn");
for (var i = 0; i < btns.length; i++) {
  btns[i].addEventListener("click", function(){
    var current = document.getElementsByClassName("active");
    current[0].className = current[0].className.replace(" active", "");
    this.className += " active";
  });
}

.filterDiv {
  float: left;
  background-color: #2196F3;
  color: #ffffff;
  width: 100px;
  line-height: 100px;
  text-align: center;
  margin: 2px;
  display: none;
}

.show {
  display: block;
}

.container {
  margin-top: 20px;
  overflow: hidden;
}

<h2>Filter DIV Elements</h2>

<select id="myBtnContainer" onchange="handleChange(event)">
  <option value='all' selected> Show all</option>
  <option value='cars'> Cars</option>
  <option value='animals'> Animals</option>
  <option value='fruits'> Fruits</option>
  <option value='colors'> Colors</option>
</select>

<div class="container">
  <div class="filterDiv cars">BMW</div>
  <div class="filterDiv colors fruits">Orange</div>
  <div class="filterDiv cars">Volvo</div>
  <div class="filterDiv colors">Red</div>
  <div class="filterDiv cars animals">Mustang</div>
  <div class="filterDiv colors">Blue</div>
  <div class="filterDiv animals">Cat</div>
  <div class="filterDiv animals">Dog</div>
  <div class="filterDiv fruits">Melon</div>
  <div class="filterDiv fruits animals">Kiwi</div>
  <div class="filterDiv fruits">Banana</div>
  <div class="filterDiv fruits">Lemon</div>
  <div class="filterDiv animals">Cow</div>
</div>

Answer 2

You can use the onChange event of a select element and also I have removed the unwanted JS code as well.

var doFilter = function(filter){
  document.querySelectorAll(".all").forEach(function(item){
    item.style.display = "none";    
  });
  document.querySelectorAll("." + filter).forEach(function(item){
    item.style.display = "block";    
  });
}

doFilter("all"); 

document.getElementById("myBtnContainer").addEventListener('change', function(e){
 doFilter(e.target.value); 
});

.all {
  float: left;
  background-color: #2196F3;
  color: #ffffff;
  width: 100px;
  line-height: 100px;
  text-align: center;
  margin: 2px;
}

.show {
  display: block;
}

.container {
  margin-top: 20px;
  overflow: hidden;
}

/* Style the buttons */
.btn {
  border: none;
  outline: none;
  padding: 12px 16px;
  background-color: #f1f1f1;
  cursor: pointer;
}

.btn:hover {
  background-color: #ddd;
}

.btn.active {
  background-color: #666;
  color: white;
}

<h2>Filter DIV Elements</h2>

<div class="container">
  <select id="myBtnContainer"> 
    <option value="all">Show all</option>
    <option value="cars">Cars</option>
    <option value="animals">Animals</option>
    <option value="fruits">Fruits</option>
    <option value="colors">Colors</option>   
  </select>
  
</div>


<div class="container">
  <div class="all cars">BMW</div>
  <div class="all colors fruits">Orange</div>
  <div class="all cars">Volvo</div>
  <div class="all colors">Red</div>
  <div class="all cars animals">Mustang</div>
  <div class="all colors">Blue</div>
  <div class="all animals">Cat</div>
  <div class="all animals">Dog</div>
  <div class="all fruits">Melon</div>
  <div class="all fruits animals">Kiwi</div>
  <div class="all fruits">Banana</div>
  <div class="all fruits">Lemon</div>
  <div class="all animals">Cow</div>
</div>