How to auto calculate?

[arteopilar]

Hello, I am really with coding. But am in need of hints and answers with my project. I need to learn how the javascript will auto compute the total cost if

total cost =delivery modes price multiply by the number of pages.
delivery modes has an equivalent price per mode

Hope someone can help with this...


Here is the html code

<html>

<head>
<title>total amount</title>
</head>

<body>
<table  id="AutoNumber5">
  <tr>
    <td>
    Delivery Modes:</td>
    <td>
    <select class="input-text" name="modes" id="modes">
	<option value ="1" selected="">7 days</option>
	<option value ="2">5 days</option>
	<option value ="3">3 days</option>
	<option value ="4">2 days</option>
    <option value ="5">24 hrs</option>
    <option value ="6">12 hrs</option>
    <option value ="7">8 hrs</option>
    <option value ="8">30-day dissertation</option>
</select></td>
  </tr>
  <tr>
    <td>
    Number of Pages:</td>
    <td>
    <select id='pages' name="pages" class="input-text"  onChange="new_Price();" >
    <option selected>2</option>
    <option value="3">3</option>
    <option value="4">4</option>
    <option value="5">5</option>
    <option value="6">6</option>
    <option value="7">7</option>
    <option value="8">8</option>
    <option value="9">9</option>
    <option value="10">10</option>
              
  </select></td>
  </tr>
  <tr>
    <td>
   Cost Per Page (USD):</td>
    <td>
    <input class="input-text" size="5" name="costperpage" readonly="readonly"/></span></td>
  </tr>
  <tr>
    <td>
    Total Amount (USD):</td>
    <td>
   <input class="input-text" id='totalamount' size="20" name="totalamount" readonly="readonly" /></span></td>
  </tr>
</table>

</body>

</html>

[gits]

you would need to call a function that would retrieve the values from the the document's nodes and does the calculation.

to retrieve a value you might use:

var val = document.getElementById('anId').value;

since you want to calculate with the values you should be aware that the retrieved values are always of type string so you might parse them as numbers when you need that with parseInt() or parseFloat() for example ...

try to make a start and post back when you have further problems with it.

kind regards

[arteopilar]

tanx for your help....