sim4ik-one,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<script>
jQuery(document).ready(function($) {
$('.quont-minus').click(function () {
var $input = $(this).next();
var val = +$input[0].defaultValue;
var count = parseInt($input.val()) - val;
count = count < val ? val : count;
$input.val(count);
$input.change();
return false;
});
$('.quont-plus').click(function () {
var $input = $(this).prev();
var val = +$input[0].defaultValue;
$input.val(parseInt($input.val()) + val);
$input.change();
return false;
});
});
</script>
</head>
<body>
<span class="quont-minus btn">-</span>
<input type="text" id="qlast_add-12-basket" value="1" size="3" onfocus="this.select()" onkeypress="return checkNumber(this, event, '1');">
<span class="quont-plus btn">+</span>
<input type="button" id="blast_add-12-basket" onclick="add2Basket('12','last_add');" value="В корзину">
</body>
</html>