perkalian

<html>
<script type="text/javascript">

 function sum() {
            var hargaa    = document.getElementById('harga').value;
            var unit      = document.getElementById('jumlah_unit').value;
            var waktu      = document.getElementById('jumlah_waktu').value;
            var total       = parseInt(hargaa) * parseInt(unit) + parseInt(waktu);
            if (!isNaN(total)) {
                 document.getElementById('total').value = total;
            };
            //document.getElementById('total').value = fullTotal;
        }

</script>
<head>
<title>bisa</title>
</head>
<body>


<h2>TEST</h2>


harga <input type="text" id="harga" onkeyup="sum();"><br>
jumlah unit <input type="number" id="jumlah_unit" onkeyup="sum();"><br>
jumlah waktu <input type="number" id="jumlah_waktu" onkeyup="sum();"><br>
total <input type="text" id="total">

</body>
</html>