Increment and Decrement price value on Change

i’m trying to do an price counter synchronizing with increment and decrement buttons, but the price is not changing when i click one of the buttons (+/-) this is not working, how can i solve this issue? Thanks!!!

$('#plus').click(function add() {
    var $qtde = $("#quantity");
    var a = $qtde.val();
    
    a++;
    $("#minus").attr("disabled", !a);
    $qtde.val(a);
});
$("#minus").attr("disabled", !$("#quantity").val());

$('#minus').click(function minust() {
    var $qtde = $("#quantity");
    var b = $qtde.val();
    if (b >= 1) {
        b--;
        $qtde.val(b);
    }
    else {
        $("#minus").attr("disabled", true);
    }
});

/* On change */
$(document).ready(function()
{
    function updatePrice()
    {
        var price = parseFloat($("#quantity").val());
        var total = (price + 1) * 1.05;
        var total = total.toFixed(2);
        $("#total-price").val(total);
    }
    $(document).on("change, keyup, focus", "#quantity", updatePrice);
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="button" value="-" id="minus" />
<input type="text" id="quantity" value="" name="quantity" />
<input type="button" value="+" id="plus" />
<br />
<input id="total-price" readonly="readonly" value=""/>

Answer

If you change your binding to update whenever there is a click on an input, you’ll get the behavior that you are expecting.

$('#plus').click(function add() {
  var $qtde = $("#quantity");
  var a = $qtde.val();

  a++;
  $("#minus").attr("disabled", !a);
  $qtde.val(a);
});
$("#minus").attr("disabled", !$("#quantity").val());

$('#minus').click(function minust() {
  var $qtde = $("#quantity");
  var b = $qtde.val();
  if (b >= 1) {
    b--;
    $qtde.val(b);
  } else {
    $("#minus").attr("disabled", true);
  }
});

/* On change */
$(document).ready(function() {
  function updatePrice() {
    var price = parseFloat($("#quantity").val());
    var total = (price + 1) * 1.05;
    var total = total.toFixed(2);
    $("#total-price").val(total);
  }
  // On the click of an input, update the price
  $(document).on("click", "input", updatePrice);
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="button" value="-" id="minus" />
<input type="text" id="quantity" value="" name="quantity" />
<input type="button" value="+" id="plus" />
<br />
<input id="total-price" readonly="readonly" value="" />