This works, does anyone see anything I shouldn't be doing?

My function that is called

function getWeight(){
        var weight;
        var quantity = document.dhform.quantity.value;
        var cardSize = document.dhform.cardSize.value;
            weight = quantity * cardSize; 
        document.rates.weight.value = weight;
    }

takes values from these drop down menues

<td><span class="style29">Quantity</span><span class="style1"><br/>
                                <select id="Quantity" name="quantity" size="1">
                                    <option value="250">250</option>
                                    <option value="500">500</option>
                                    <option value="1000" selected>1000</option>
                                    <option value="1500">1500</option>
                                    <option value="2000">2000</option>
                                    <option value="2500">2500</option>
                                    <option value="3000">3000</option>
                                    <option value="4000">4000</option>
                                    <option value="5000">5000</option>
                                </select>
                            </span></td>
<td><p><span class="style1"><span class="style29">Size</span><br/>
                                      <select id="Size" name="Size" size="1" onChange="getWeight()">
                                        <option value="0.00999" selected>8.5 x 3.5</option>
                                        <option value="0.0146">11 x 4</option>
                                      </select>
                            </span></p></td>

Value needs to be inserted into this text box

<td style="width: 115px; height: 49px;"><span class="style16">Weight</span><br/>
                                  <input type="text" id="weight" name="weight" size="10" maxlength="4"/>
                              </td>

This works, does anyone see anything I shouldn't be doing?

My function that is called

function getWeight(){
        var weight;
        var quantity = document.dhform.quantity.value;
        var cardSize = document.dhform.cardSize.value;
            weight = quantity * cardSize; 
        document.rates.weight.value = weight;
    }

takes values from these drop down menues

<td><span class="style29">Quantity</span><span class="style1"><br/>
                                <select id="Quantity" name="quantity" size="1">
                                    <option value="250">250</option>
                                    <option value="500">500</option>
                                    <option value="1000" selected>1000</option>
                                    <option value="1500">1500</option>
                                    <option value="2000">2000</option>
                                    <option value="2500">2500</option>
                                    <option value="3000">3000</option>
                                    <option value="4000">4000</option>
                                    <option value="5000">5000</option>
                                </select>
                            </span></td>
<td><p><span class="style1"><span class="style29">Size</span><br/>
                                      <select id="Size" name="Size" size="1" onChange="getWeight()">
                                        <option value="0.00999" selected>8.5 x 3.5</option>
                                        <option value="0.0146">11 x 4</option>
                                      </select>
                            </span></p></td>

Value needs to be inserted into this text box

<td style="width: 115px; height: 49px;"><span class="style16">Weight</span><br/>
                                  <input type="text" id="weight" name="weight" size="10" maxlength="4"/>
                              </td>

• javascript
• html
• forms

Share Improve this question Follow edited Feb 10, 2014 at 16:11 BenMorel 36.8k5252 gold badges206206 silver badges337337 bronze badges asked Apr 30, 2010 at 14:55 shinjuoshinjuo 21.1k2424 gold badges7676 silver badges104104 bronze badges 4

• This is too general and sounds like "How do I use javascript?". Please be more specific. – D'Arcy Rittich Commented Apr 30, 2010 at 14:58
• you need ajax i think, you can google about it or be more specific to your question with sample code you are using. – Sarfraz Commented Apr 30, 2010 at 14:59
• Ajax may well not be necessary; where Ajax es in is if the determination of the updated value requires going back to the server to fetch data. In many cases it doesn't. – Jacob Mattison Commented Apr 30, 2010 at 15:01
• Not easy to explain myself anymore than I did when I do not even know what I am lookng for. I am not looking for an answer just a point in a direction – shinjuo Commented Apr 30, 2010 at 15:10

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 2

Yes, it's done with Javascript. Let's say the "choose something" part is a drop-down (an HTML select box). You add an "onchange" event handler to that select box which fires a javascript function (which will automatically get the changed select box element as a parameter). Within that function, you use the value of the select box to determine what you want the value of the other box to be, and you update that other box's value.

Example:

<head>
<script language="JavaScript">
    function setToy(dropDown) {
        var pet = dropDown.options[dropDown.selectedIndex].value);
        var newBox = document.getElementById("toy");
        var toyText = "";
        switch(pet) {
           case "dog": toyText = "bone";
           case "cat": toyText = "mouse";
           default:toyText = "";
        }
        newBox.innerHTML = toyText;
    } 
</script></head>
<body>
<select name="petDropDown" onChange="updateToy(this)">
    <option value="dog">Dog</option>
    <option value="cat">Cat</option>
</select><br />
Preferred Toy: <input id="toy" />
</body>

I'll add that if you do this stuff a lot, you should look into jQuery, which makes this kind of thing much easier.