How to do reverse value alert using for statement

Hi,

Could someone advise me how to do the reverse values in this code? 300, 200, 100. Think I'm really hopeless when come to programming :-(

for (intIndex = 0; intIndex > ayrElements.length ;intIndex--)// this is the part that I'm stuck.

Here's the code:

Expand|Select|Wrap|Line Numbers

 <html>

<head>

<style>

#divMessage { width : 500px;

    height : 30px;

    border : 1px solid black;

    }
 
body { font : arial;

    font-size : 10px;}
 
</style>

<script language="javascript">
 
  function inspectCheckBoxes(){    
 
   var aryElements = new Array(); 

   var intValue = new Number(0); 

   var intIndex  = new Number(0); 
 
     aryElements = document.getElementsByName("chkData");
 
   for (intIndex= 0 ;intIndex <aryElements.length;intIndex++){

    if (aryElements[intIndex].checked)

               alert(aryElements[intIndex].value);

   }

}

</script>

</head>

<body>

<table border="1">

  <tr>

   <td colspan="2">

    <b>Experiment 1</b><br>

    Experiment using JavaScript to communicate and 

    control the checkbox controls.</td>

  </tr>

  <tr>

    <td style="width:10%"><input type="checkbox" name="chkData" value="100"/></td>

    <td>100</td>

  </tr>

<tr>

    <td><input type="checkbox" name="chkData" value="200"/></td>

    <td>200</td>

  </tr>

  <tr>

    <td><input type="checkbox" name="chkData" value="300"/></td>

    <td>300</td>

  </tr>

  <tr>

     <td colspan="2">

     <div id="divMessage" ></div>

     </td>

  </tr> 

  <tr>

    <td colspan="2" align="right">

     <input type="button" id="btnExperiment" value="Experiment" onclick="inspectCheckBoxes()" >

    </td>

  </tr>

</table>

</body>

</html>

Jan 19 '10 #1

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2334

Dormilich

8,658

Expert Mod 8TB

for (intIndex = 0; intIndex > ayrElements.length ;intIndex--)

let’s apply some common logic:

if you count down, do it from the largest value to the smallest value.

counting down from 0 will get you in negative numbers …
quitting the loop when the counter variable is above the maximum value … is a condition you never reach with decrementing

try it, it should be easier now.

Jan 19 '10 #2

tangara

Hi,

It doesn't work. I run it and nothing happens.

By right, it should give me alert message of 300, 200, 100.

:-(

Jan 19 '10 #3

Plater

7,872

Expert 4TB

Well even when you do understand how for loops work (http://www.javascriptkit.com/javatutors/loop3.shtml), is the "collection of objects" returned by getElementsByName() garunteed to be in the same order all the time?

Jan 19 '10 #4

Dormilich

8,658

Expert Mod 8TB

let me guess … you didn’t select any checkbox?

Jan 19 '10 #5

Dormilich

8,658

Expert Mod 8TB

Well even when you do understand how for loops work, is the array returned by getElementsByName() garunteed to be in the same order all the time?

a) it’s not an Array
b) NodeLists are in document order

EDIT: some thougths on the code

Expand|Select|Wrap|Line Numbers

 function inspectCheckBoxes(){    

   // unnecessary, aryElements’ type will be set later

   var aryElements = new Array(); 

   // not used, why define?

   var intValue = new Number(0); 

   // var intIndex = 0 would have been sufficient

   var intIndex  = new Number(0); 
 
   // declare the variable here: var elements = document…

     aryElements = document.getElementsByName("chkData");
 
   // avoid calculations in the abort condition part, i.e. calculate the length only once:

   // for (var i=0, l<elements.length; i<l, i++)

   for (intIndex= 0 ;intIndex <aryElements.length;intIndex++){

    // it’s good coding practice to wrap every code block of if in { } even if it is only one line

    if (aryElements[intIndex].checked)

               alert(aryElements[intIndex].value);

   }

}

Jan 19 '10 #6

Dormilich

8,658

Expert Mod 8TB

after dorm's nitpicking:
is the "collection of objects" returned by getElementsByName() garunteed to be in the same order all the time?

yes, it is.

Jan 19 '10 #7

tangara

I have found the solution already.

Just use :-

Expand|Select|Wrap|Line Numbers

 
for(intIndex=aryElements.length-1; intIndex>=0; intIndex--){

alert(aryElements[intIndex].value)

}

Jan 20 '10 #8

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How to do reverse value alert using for statement

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