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makanan 1 <input type="text" id="txt1" onkeyup="sum();"/> .
makanan 2 <input type="text" id="txt2" onkeyup="sum();"/> .
makanan 3 <input type="text" id="txt3" onkeyup="sum();"/> .
minuman 1 <input type="text" id="txt4" onkeyup="sum();"/> .
minuman 2 <input type="text" id="txt5" onkeyup="sum();"/>
minuman 3 <input type="text" id="txt6"/> total
<script>function sum() {
var txtFirstNumberValue = document.getElementById('txt1').value;
var txtSecondNumberValue = document.getElementById('txt2').value;
var txtThreeNumberValue = document.getElementById('txt3').value;
var txtFourNumberValue = document.getElementById('txt4').value;
var txtFiveNumberValue = document.getElementById('txt5').value;
var result = parseFloat(txtSecondNumberValue) + parseInt(txtFirstNumberValue);
var result = parseFloat(txtThreeNumberValue) + parseInt(txtSecondNumberValue);
var result = parseFloat(txtFourNumberValue) + parseInt(txtThreeNumberValue);
var result = parseFloat(txtFiveNumberValue) + parseInt(txtThreeNumberValue);
if (isNaN(result)) {
var document.getElementById('txt6').value = result;
}
}
</script>