Using prototype.js its very easy to implement Ajax (Asynchronous javascript and xml). Just call the specific function from html and then parse the xml that is returned from php.

Here is an example. in this example, we are calling a function in the onChange event of a dropdown box.

<tr>

<td>
<select name=”product_name” id=”product_name” style=”width:165px” onChange=”showprice();”>
<option value=”">Select One</option>
<?php
$searchcategory = “select product_name, product_id from product”;
$searchquery = mysql_query($searchcategory);
while($row=mysql_fetch_row($searchquery))
{
echo ‘<option>’.$row[0].’</option>’;
}
?>
</select>
</td>
<td align=right>
<label class=”label” id=lbl_product_price name=lbl_product_price> Price </label>
</td>
<td>
<input readonly type=”text” class=”text” id=”product_price” name=”product_price” value=”">
</td>

</tr>

in html head tag include this line

<script language=”JavaScript” src=”prototype.js” mce_src=”prototype.js”></script>

Now in the javacript part, i’ll use prototype.js , and here is how to use it. you can download prototype.js from internet.

function showprice()
{
checkavailability();
var url = ’sales1.php’;
var proname = $F(’product_name’);
var pars = ‘cmd=loadPrice&name=’ + proname;
//alert(pars);
var myAjax = new Ajax.Request(url, {method: ‘get’, parameters: pars, onComplete: showResponse});
}

Now in php file (sales1.php) , just return product price …

if(cmd==loadPrice) //// [note: we have passed cmd = loadPrice in javascript part ]

{

$product_name = $_REQUEST['product_name'];

$statement =”select product_price from product where product_name=$product_name”;

$result = mysql_query($statement);

$row = mysql_fetch_object($result);

return $row->product_price;

}

Now parse the return value in javascript showResponse function

function showResponse(serverResponse){

if(serverResponse.responseText){
$(’product_price’).value = parseInt(serverResponse.responseText);

// if you want to show the price in a div or in a td then you should use $(’product_price’).innerHTML in place of $(’product_price’).value //
}
}

That’s all. Enjoy