CSS: Error in Toggle Classes By using Class name

Question

i am trying to toggle classes by using class name. My code is working fine when i am toggling using id . how can i make it work only one red should be visible at one time.

CODEPEN

HTML:

<div  class="mainmenu "onclick="hideshowmenu()">RED1</div>
         <div id="submenu" class="submenu">
           
            <div  class="mainmenu "onclick="hideshowmenu()">RED2</div>
         <div id="box" class="box">

js:

function hideshowmenu() {

var element = document.getElementsByClassName("box");
element.classList.toggle("bg-red");
}

CSS:

.bg-red{
  margin-top:10px;
  background-color:red;
  height:20px;
}

Answer 1

As the name of getElementsByClassName suggest, it returns element S , so you are getting HTMLCollection, not one element. Query the first one, like this:

function hideshowmenu() {
  var element = document.getElementsByClassName("box")[0];
  element.classList.toggle("bg-red");
}

or:

function hideshowmenu() {
  var elements = document.getElementsByClassName("box");
  elements[0].classList.toggle("bg-red");
}

Answer 2

What is returned by document.getElementsByClassName("box"); is a collection. You need to specify the index to access the classList property.

You are doing:

var element = document.getElementsByClassName("box");
element.classList.toggle("bg-red");

When you should be doing

var element = document.getElementsByClassName("box");
element[0].classList.toggle("bg-red");

You could also loop through the elements if you want to toggle multiple values.

Example code fiddle https://jsfiddle.net/agy5jtb0/1/

Answer 3

getElementsByClassName("box") return a collection of elements, but you considered it as a single element that is your mistake. I suggest something like this:

html :

<div class="mainmenu " onclick="hideshowmenu(this)">RED1</div>
<div id="submenu" class="submenu">
    <div class="mainmenu" onclick="hideshowmenu(this)">RED2</div>
    <div id="box" class="box"></div>
</div>

js :

function hideshowmenu(el) {
    el.classList.toggle("bg-red");
}

Answer 4

Check this (not sure If is this what you need):

 function hideshowmenu() { var elements = document.getElementsByClassName("box"); for (let a of elements) { a.classList.toggle("bg-red"); } }

 .bg-red{ margin-top:10px; background-color:red; height:20px; }

 <div class="mainmenu " onclick="hideshowmenu(this)">RED1</div> <div id="submenu" class="submenu"> <div class="mainmenu" onclick="hideshowmenu(this)">RED2</div> <div id="box" class="box"></div> </div>