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Asked: 2026-05-19T00:37:45+00:00

I need some help finding the error in my javascript calculation. I need to

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I need some help finding the error in my javascript calculation.

I need to calculate the sum of my input boxes automatically and have my user be able to edit the calculation using + or – buttons.

The code I have already does the calculation automatically if you manually enter the numbers, but pressing the + or – does not change the calculation.

Here is the code:

<html>
<head>
<script language="javascript">
function Calc(className){
var elements = document.getElementsByClassName(className);
var total = 0;

for(var i = 0; i < elements.length; ++i){
total += parseInt(elements[i].value);
}

document.form0.total.value = total;
}

function addone(field) {
field.value = Number(field.value) + 1;
}

function subtractone(field) {
field.value = Number(field.value) - 1;
}
</script>

</head>
<body>
<form name="form0" id="form0">

1: <input type="text" name="box1" id="box1" class="add" value="0" onKeyUp="Calc('add')" onChange="updatesum()" onClick="this.focus();this.select();" />
<input type="button" value=" + " onclick="addone(box1);">
<input type="button" value=" - " onclick="subtractone(box1);">
<br />

2: <input type="text" name="box2" id="box2" class="add" value="0" onKeyUp="Calc('add')" onClick="this.focus();this.select();" />
<input type="button" value=" + " onclick="addone(box2);">
<input type="button" value=" - " onclick="subtractone(box2);">
<br />

3: <input type="text" name="box3" id="box3" class="add" value="0" onKeyUp="Calc('add')" onClick="this.focus();this.select();" />
<input type="button" value=" + " onclick="addone(box3);">
<input type="button" value=" - " onclick="subtractone(box3);">
<br />

<br />
Total: <input readonly style="border:0px; font-size:14; color:red;" id="total" name="total">

</form>
</body></html>

Im sure the issue must be small, I just cant put my finger on it.

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1 Answer

  1. Editorial Team

    One easy way is to update the sum when you click the buttons. You can add Calc('add') to the onclick event, or to the addone and subtractone functions (You probably want to add the class as a parameter though). For example:

    function addone(field) {
  field.value = Number(field.value) + 1;
  Calc('add');
}

function subtractone(field) {
  field.value = Number(field.value) - 1;
  Calc('add');
}

    Working example: http://jsbin.com/umimu4/

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