<!DOCTYPE html> <html> <head> <title>Untitled</title> <meta charset="utf-8"> <script> window.addEventListener('DOMContentLoaded', function() { var form = document.querySelector('form'); form.addEventListener('input', function() { var price = +form.price.value || 0; var amount = +form.amount.value || 0; form.sum.value = price * amount }); }); </script> </head> <body> <form> <div> <span>Цена товара</span> <input name="price" type="text"></input> </div> <div> <span>Количество</span> <input name="amount" type="text"></input> </div> <div> <span>Сумма транзакции</span> <input name="sum" type="text"></input> </div> </form> </body> </html>
var dostavka= form.dostavka.checked? +form.dostavka.value : 0;
