Buttons Plus & Minus

How to increment or decrement a form field using jQuery, specially useful for quantity fields.

HTML

<form id='myform' method='POST' action='#'>
    <p>Помада</p>
    <span>Стоимость</span>
    <input type='text' value='300' name="sto" class="sto" disabled >
    <span>Кол-во</span>
    <input type='text' value='1' name="kolvo" class="kolvo">
    <p>цена</p>
    <input type='text' value="" name="cena" class="cena">
</form>

JavaScript

jQuery(document).ready(function(){
$(".sto,  .kolvo").on('input', function() {
  $(".cena").val($sto*$kolvo);
});
});