Opdatere værdifelt ved afkrydsning af felt

F.eks.

<form>
<input type="text" name="amount" value="0"><br>
0.25 <input type="checkbox" value="0.25" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
0.50 <input type="checkbox" value="0.50" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
0.75 <input type="checkbox" value="0.75" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
1.00 <input type="checkbox" value="1.00" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
1.25 <input type="checkbox" value="1.25" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
1.50 <input type="checkbox" value="1.50" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
1.75 <input type="checkbox" value="1.75" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
2.00 <input type="checkbox" value="2.00" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
2.25 <input type="checkbox" value="2.25" onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);"><br>
</form>

<form action='?' id='tilkoeb' name='tilkoeb' method='post' style='display: inline;'><table><tr><td></td><td style='width: 350px;'><p>Produkt</p></td><td><p>Pris</p></td></tr><tr>
                <td><input onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);" type="checkbox" name="gul" value="6.00"></td><td><p><font style='background-color: yellow;'>Gul baggrund</font> på skrift i auktionoversigt</p></td><td><p>6,00 kr</p></td>
            </tr><tr>
                <td><input onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);" type="checkbox" name="fed" value="4.00"></td><td><p><strong>Fed</strong> skrift i auktionsoversigt</p></td><td><p>4,00 kr</p></td>

            </tr><tr>
                <td><input onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);" type="checkbox" name="pic1" value="6.00"></td><td><p>Et ekstra billede af varen.<br />Kan <i>ikke</i> kombineres med to ekstra billeder</p></td><td><p>6,00 kr</p></td>
            </tr><tr>
                <td><input onclick="this.form.amount.value=(this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value);" type="checkbox" name="pic2" value="10.00"></td><td><p>To ekstra billeder af varen.<br />Kan <i>ikke</i> kombineres med et enkelt ekstra billede</p></td><td><p>10,00 kr</p></td>

            </tr></table></form><p>Du har nu valgt produkter for: <input type='text' name='amount' value='0'>


min Firefox javascript debugger siger:
Error: this.form.amount has no properties.


hvad er der i vejen?

Ah </form> var i vejen.
Hvordan gør det så der er altid er to decimaler på?

Indsæt denne:

<script language="javascript" type="text/javascript">
function afrund(tal){
  if(isNaN(tal))return "0,00";
  tal = ""+(Math.round(tal*100))/100;
  punktum = tal.indexOf(".");
  if (punktum==-1)return tal+".00";
  if (tal.length-punktum==3)return tal;
  else return tal+"0";
}
</script>

-- og gør:

<td><input onclick="this.form.amount.value=afrund((this.checked)?+this.form.amount.value+ +this.value:+this.form.amount.value-(+this.value));" type="checkbox" name="pic2" value="10.00"></td><td><p>To ekstra billeder af varen.<br />Kan <i>ikke</i> kombineres med et enkelt ekstra billede</p></td><td><p>10,00 kr</p></td>

Tak. Smider du et svar?

Velbekomme '-)

-- og tak for point ;~}