How to sum a price based on quantity amount

Question

I am trying to create a input for Quantity (Plus/Minus Buttons) but I can't get it to sum up the price when a different quantity is chosen.

For example, if the item is £2.00 and 2x quantity is chosen then it should display £4.00 instead

Here is what I have so far..

function increaseCount(a, b) {
  var input = b.previousElementSibling;
  var value = parseInt(input.value, 10);
  value = isNaN(value) ? 0 : value;
  value++;
  input.value = value;
}
function decreaseCount(a, b) {
  var input = b.nextElementSibling;
  var value = parseInt(input.value, 10);
  if (value > 1) {
    value = isNaN(value) ? 0 : value;
    value--;
    input.value = value;
  }
}


$('#quantity').change(function (event) {
     $('#price').html($(this).val() * parseInt($('#price').text(), 10));
 });

.counter {
    width: 150px;
    margin: auto;
    display: flex;
    align-items: center;
    justify-content: center;
}
.counter input {
  background:none;
  margin:0px 12px;
  width:80px;
  border:1px solid #0052cc;
  line-height:34px;
  font-size:20px;
  text-align:center;
  color:var(--text-color);
  appearance:none;
  outline:0;
}
.counter span {
    background:#0052cc;
    display: block;
    font-size: 25px;
    padding:0 10px;
    cursor: pointer;
    color:#111;
    user-select: none;
}

<div class="counter">
  <span class="down" onClick='decreaseCount(event, this)'>-</span>
  <input type="text" id="quantity" value="1" name="quantity">
  <span class="up" onClick='increaseCount(event, this)'>+</span>
</div>


Price: £<span id="price" value="2.00"></span>2.00

Answer 1

The "updateTotalPrice" function is called from within the "increaseCount", "decreaseCount", and "change" event listeners to ensure that the total price is always up-to-date. The "price" element is used to display the calculated total, which is formatted to two decimal places using the "toFixed" method.

function increaseCount(a, b) {
  var input = b.previousElementSibling;
  var value = parseInt(input.value, 10);
  value = isNaN(value) ? 0 : value;
  value++;
  input.value = value;
  updateTotalPrice();
}

function decreaseCount(a, b) {
  var input = b.nextElementSibling;
  var value = parseInt(input.value, 10);
  if (value > 1) {
    value = isNaN(value) ? 0 : value;
    value--;
    input.value = value;
    updateTotalPrice();
  }
}

function updateTotalPrice() {
  var quantity = parseInt($('#quantity').val(), 10);
  var price = parseFloat($('#price').attr('value'));
  var total = quantity * price;
  $('#price').text(total.toFixed(2));
}

$(document).ready(function() {
  // set up event listeners
  $('#plus-btn').click(function(event) {
    increaseCount(event, this);
  });
  $('#minus-btn').click(function(event) {
    decreaseCount(event, this);
  });
  $('#quantity').change(function(event) {
    updateTotalPrice();
  });
  
  // update total price on page load
  updateTotalPrice();
});

.counter {
    width: 150px;
    margin: auto;
    display: flex;
    align-items: center;
    justify-content: center;
}
.counter input {
  background:none;
  margin:0px 12px;
  width:80px;
  border:1px solid #0052cc;
  line-height:34px;
  font-size:20px;
  text-align:center;
  color:var(--text-color);
  appearance:none;
  outline:0;
}
.counter span {
    background:#0052cc;
    display: block;
    font-size: 25px;
    padding:0 10px;
    cursor: pointer;
    color:#111;
    user-select: none;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="counter">
  <span class="down" onClick='decreaseCount(event, this)'>-</span>
  <input type="text" id="quantity" value="1" name="quantity">
  <span class="up" onClick='increaseCount(event, this)'>+</span>
</div>


Price: £<span id="price" value="2.00"></span>