how can I show the number of items in an shopping card icon from javascript

I have a shopping cart icon from FontAwesome in which I want to assign the sum of items selected from inputs. I’ve added the number of items using a JavaScript function but I can’t manage to show this number into the icon content.

The content value of the icon is taken from the HTML attribute value="" as specified in the CSS content:attr(value).

How can I modify it to be the value of the JavaScript variable totalQty?

I used document.getElementsByClassName("badge").value = totalQty; but it doesn’t work.

Here is my code:

.badge:after {
  content: attr(value);
  font-size: 12px;
  color: #fff;
  background: red;
  border-radius: 50%;
  padding: 0 5px;
  position: relative;
  left: -8px;
  top: -10px;
  opacity: 0.9;
}

<i class="fa badge fa-lg" id="card-qty" value=""></i>

Answer

You can do it with js by targeting the ID instead of the class and do it like this:

var totalQty = 5;
var elementVar = document.getElementById("card-qty");
elementVar.setAttribute("value", totalQty);

So here it is working.

var totalQty = 5;
var elementVar = document.getElementById("card-qty");
elementVar.setAttribute("value", totalQty);

.badge:after {
  content: attr(value);
  font-size: 12px;
  color: #fff;
  background: red;
  border-radius: 50%;
  padding: 0 5px;
  position: relative;
  left: -8px;
  top: -10px;
  opacity: 0.9;
}

<i class="fa badge fa-lg" id="card-qty" value=""></i>

EDIT: If you are set on getting the elements by class instead of ID you can use this js code:

var totalQty = 5;
const elementVar = document.getElementsByClassName("badge");
let index = 0;


while (index < elementVar.length) {
  elementVar[index].setAttribute("value", totalQty);
  index++
}

Here it is working:

var totalQty = 5;
const elementVar = document.getElementsByClassName("badge");
let index = 0;


while (index < elementVar.length) {
  elementVar[index].setAttribute("value", totalQty);
  index++
}

.badge:after {
  content: attr(value);
  font-size: 12px;
  color: #fff;
  background: red;
  border-radius: 50%;
  padding: 0 5px;
  position: relative;
  left: -8px;
  top: -10px;
  opacity: 0.9;
}

<i class="fa badge fa-lg" id="card-qty" value=""></i>