Create shopping cart using javascript

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Javascript

CSS3

HTML5

WebAPI

hello
I am coding an online-shopping system Cart with JavaScript. my problem is to update Total Price, when the product quantity changes, I don Not know how to do that. related codes are:

HTML:

<div class="product-price" style="margin-left:60px;"></div>

<div class="quantity">
  <button class="plus-btn" type="button" name="button">
      <img src="../img/svg/PlusQ.png" alt="" />
  </button>
   
  <input type="text" name="name" value="1">

  <button class="minus-btn" type="button" name="button">
    <img src="../img/svg/MinusQ.png" alt="" />
  </button>
                            
<div class="total-price">&lt;label>&lt;/label></div>

JS:

$('.minus-btn').on('click', function (e) {
    e.preventDefault();
    var $this = $(this);
    var $input = $this.closest('div').find('input');
    var $totalprice = $this.closest('div').find('lable'); // I have problem with this line
    var value = parseInt($input.val());

    if (value != 1) {
        value = value - 1;
    } else {
        value = 0;
    }

    $input.val(value);
    $totalprice.innerHTML = value * 2; // Testing if Total price works, It Does NOT

});

$('.plus-btn').on('click', function (e) {
    e.preventDefault();
    var $this = $(this);
    var $input = $this.closest('div').find('input');
    var value = parseInt($input.val());

    if (value != 100) {
        value = value + 1;
    } else {
        value = 100;
    }

    $input.val(value);
});

What I have tried:

in fact, I do not know how to access .product-price and .total-price that are a "div" element before and after the current "div".