[SOLVED] Forms and JS

[ManifestX]

Hello there. I'm new, and I have some questions on creating a variable, which takes a value, "quantity", and whatever number you input, multiplies them, then outputs it to "amountNum". I've used onChange, but there is no value displayed in that field. I don't know what it is that's wrong with my code and was hoping you could help.

 

Here's my code so far:

 

...
      <SCRIPT language=Javascript>
      <!--
      function getAmount(quantity, num)
      {
         return quantity*num;
      }
      //-->
      </SCRIPT>
...
<td> <INPUT align="right" id="txtChar" onkeypress="return isNumberKey(event)" type="text" maxlength="3" size="1" name="quantity" value="0">  </td>
<td>x$2.50</td>
<td> <INPUT align="right" id="amntChng" onchange="this.quantity.getAmount(this.quantity.value, 2.50)" type="text" maxlength="6" size="1" name="amountNum" disabled="disabled">  </td>
...

[KevinM1]

JavaScript is a bit different than other languages.  Returning a value doesn't stick it in an element.  Also, the way you're attempting to use events is a bit weird.  You simply need:

 

<script type="text/javascript">
   window.onload = function(){
      var quantity = document.getElementById('txtChar');
      var amount = document.getElementById('amntChng');

      quantity.onchange = function(){
         amount.value = this.value * 2.50;  //you may need amount.innerHTML = this.value * 2.50 instead
      }
   }
</script>

...

<td><input id="txtChar" /></td>
<td><input id="amntChng" /></td>

 

A couple of key ideas here:

 

I don't like mixing JS and HTML.  It's a style choice, but in my experience, things are easier to fix/manage/edit/maintain if markup and script are separate.  So, my solution does away with inline JS calls in the HTML.  To put it another way, you wouldn't need to add events (i.e., onchange) to the elements themselves within the HTML.

 

The code isn't necessarily complete.  It should show you how to approach the problem, however.

[ManifestX]

Thank you Nightslyr, I was able to finish it with your help.

Cheers!