Скрипт
<script type="text/javascript">
function getSum()
{
var var1 = parseFloat(document.getElementById('<? echo $arItemIDs['PRICE']; ?>').value);
var var2 = parseFloat(document.getElementById('<? echo $arItemIDs['QUANTITY']; ?>').value);
return document.getElementById('sum').value = var1 * var2;
}
</script>
Поле цены
<div onchange='getSum()' class="item_current_price" id="<? echo $arItemIDs['PRICE']; ?>"><? echo $arResult['MIN_PRICE']['PRINT_DISCOUNT_VALUE']; ?></div>
Поле кол-ва
<span class="item_buttons_counter_block">
<a href="javascript:void(0)" class="bx_bt_button_type_2 bx_small bx_fwb" id="<? echo $arItemIDs['QUANTITY_DOWN']; ?>">-</a>
<input id="<? echo $arItemIDs['QUANTITY']; ?>" type="text" class="tac transparent_input" onchange='getSum()' value="<? echo (isset($arResult['OFFERS']) && !empty($arResult['OFFERS'])
? 1
: $arResult['CATALOG_MEASURE_RATIO']
); ?>">
<a href="javascript:void(0)" class="bx_bt_button_type_2 bx_small bx_fwb" id="<? echo $arItemIDs['QUANTITY_UP']; ?>">+</a>
<span class="bx_cnt_desc" id="<? echo $arItemIDs['QUANTITY_MEASURE']; ?>"><? echo (isset($arResult['CATALOG_MEASURE_NAME']) ? $arResult['CATALOG_MEASURE_NAME'] : ''); ?></span>
</span>
Как сделать подсчет по умолчанию, т.е без событий что есть в поле то и множит