[Javascript] Adding checkbox values

[Hassan Schroeder]

Alan Easton wrote:

> I am trying something which I think is simple. I have a form with 9 
> checkboxes and a text box. Each checkbox has a numeric value.
> 
> Now all I want to do is add them up when they get ticked, and the total 
> value to appear in the text field, or subtract the value of the checkbox 
> from the total if it is unchecked. I want this to happen automatically.
> 
> Here is what I am trying, but as yet it is not working.

> function calculate(what) {
>    for (var i=1,answer=0;i<9;i++)
>        answer += what.elements['Checkbox' + i].value - 0;
>    what.answer.value = answer;
> }

A checkbox has a value, and a 'checked' attribute of true or false;
they aren't related. So you're adding the values for *all* the boxes,
regardless of whether they're checked. Well, actually, one less than
all, since your loop starts at 1 and ends at 8 :-)

> <form ID="Form2">
> <INPUT type="checkbox" ID="Checkbox1" NAME="Checkbox1" VALUE="1" 
> onchange="calculate(this.form)">

You might want to avoid all the looping, and use a global variable
for the value to pass to your display field; something like --

<script type="text/javascript">
var calculatedValue = 0;
function calculate(what) {
	var change = 0;
	change = ( what.checked )? (what.value - 0) : (0 - what.value);
	calculatedValue = calculatedValue + change;
	document.getElementById("Text13").value = calculatedValue;
}
</script>

Note the change in the onchange here:

	<input  onchange="calculate(this)">

HTH!
-- 
Hassan Schroeder ----------------------------- hassan at webtuitive.com
Webtuitive Design ===  (+1) 408-938-0567   === http://webtuitive.com

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