Assigning values to check boxes and adding the numbers

The following routine adds a number to the total each time the checkbox with an assigned number is checked. This works perfectly (Example 1). But when I try to assign a variable that was calculated previously (Example 2), it returns a NaN in the Total, Can someone help me fix this? Thanks.

Example 1. This works

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<script type="text/javascript">

    function checkTotal() {

        document.listForm.total.value = '';

        var sum = 0;

        for (i=0;i<document.listForm.choice.length;i++) {

          if (document.listForm.choice[i].checked) {

              sum = sum + parseInt(document.listForm.choice[i].value);

          }

        }

        document.listForm.total.value = sum;

    }

</script>
 
<form name="listForm">

<input type="checkbox" name="choice" value="2" onchange="checkTotal()"/>2<br/>

<input type="checkbox" name="choice" value="5" onchange="checkTotal()"/>5<br/>

<input type="checkbox" name="choice" value="10" onchange="checkTotal()"/>10<br/>

<input type="checkbox" name="choice" value="20" onchange="checkTotal()"/>20<br/>

Total: <input type="text" size="2" name="total" value="0"/>

</form>

Example 2. This returns a NaN in the Total field

Expand|Select|Wrap|Line Numbers

 
<script type="text/javascript">

    function checkTotal() {

        document.listForm.total.value = '';

        var sum = 0;

        for (i=0;i<document.listForm.choice.length;i++) {

          if (document.listForm.choice[i].checked) {

              sum = sum + parseInt(document.listForm.choice[i].value);

          }

        }

        document.listForm.total.value = sum;

    }

</script>
 
<form name="listForm">

<input type="text" name="Item1cost" value="2" >2

<input type="checkbox" name="choice" value="Item1cost" onchange="checkTotal()"/><br>
 
<input type="text" name="Item2cost" value="5" >5

<input type="checkbox" name="choice" value="Item2cost " onchange="checkTotal()"/><br>
 
<input type="text" name="Item3cost " value="5" >5 

<input type="checkbox" name="choice" value="Item3cost" onchange ="checkTotal()"/> <br>
 
<input type="test" name="Item4cost" value="20">20

<input type="checkbox" name="choice" value="Item4cost" onchange="checkTotal()"/> <br>
 
Total: <input type="text" size="4" name="total" value="0"/>

</form>

Nov 19 '11 #1

Subscribe Reply

✓ answered by Dormilich

taking the snippet from above:

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 var box = document.getElementsByName("choice")[0];

alert(box.value);

var txt = document.getElementsByName(box.value)[0];

alert(txt.value);
 
// or

var box = document.listForm.choice[0];

var txt = document.listForm[box.value]; // since there is only one such name

alert(txt.value);

3761

Dormilich

8,658

Expert Mod 8TB

it’s a wrong assumption that you can in the value reference a number from another element.

Expand|Select|Wrap|Line Numbers

 <input type="text" name="Item1cost" value="2" >2

<input type="checkbox" name="choice" value="Item1cost" onchange="checkTotal()"/>

the value of the checkbox is the string "Item1cost" which obviously is parsed as NaN.

what you would need to do is taking the value from the checkbox and using that for fetching the value of the element that has this ID/name.

Nov 20 '11 #2

jamming

I'm sorry, I don't understand. Can you give me an example? Thanks.

Nov 20 '11 #3

Dormilich

8,658

Expert Mod 8TB

taking the snippet from above:

Expand|Select|Wrap|Line Numbers

 var box = document.getElementsByName("choice")[0];

alert(box.value);

var txt = document.getElementsByName(box.value)[0];

alert(txt.value);
 
// or

var box = document.listForm.choice[0];

var txt = document.listForm[box.value]; // since there is only one such name

alert(txt.value);

Nov 21 '11 #4

jamming

Thanks so much. It makes so much sense once you showed me how to do it..

Nov 21 '11 #5

jamming

Well it wasn't easy for someone who doesn't know Javascript, nor is it intuitive. I had to deal with parsing the text that converted it to numbers. For anyone wanting to do this, here's the code with the help of "Dormillich". It still took me half a day to figure it out.

Expand|Select|Wrap|Line Numbers

 
<html>

<head>

<script type="text/javascript">

function checkTotal() {

    document.listForm.total.value = '';

    var sum = 0;

    for (i=0;i<document.listForm.choice.length;i++) {

         if (document.listForm.choice[i].checked) {

    var box = (document.listForm.choice[i]);

        alert(box.value);

    var txt = (document.listForm[box.value]); 

           alert(txt.value);

    sum = sum + parseInt(txt.value) ;    

           alert(sum);

           }

    }

     document.listForm.total.value = sum;

}

</script>
 
<form name="listForm">

<input type="text" name="Item1cost" value="2" >2

<input type="checkbox" name="choice" value="Item1cost" onChange="checkTotal()"/><br>
 
<input type="text" name="Item2cost" value="5" >5

<input type="checkbox" name="choice" value="Item2cost" onChange="checkTotal()"/><br>
 
<input type="text" name="Item3cost" value="5" >5 

<input type="checkbox" name="choice" value="Item3cost" onchange ="checkTotal()"/> <br>
 
<input type="test" name="Item4cost" value="20">20

<input type="checkbox" name="choice" value="Item4cost" onChange="checkTotal()"/> <br>
 
Total: <input type="text" size="10" name="total" value="0"/>

</form>

</body>

</html>

Nov 22 '11 #6

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