Ajax - Javascript Techniques
The real trick of Ajax is updating a segment of the page without actually
having to reload the entire page. This little trick is often done by utilizing a
Javascript property known as innerHTML. Each HTML element on a page
has an innerHTML associated with it that can be changed at any time.
For us, we need to update it when our ajax-example.php script has finished executing.
Updating the order.html Page
First we need to create a new div on this page that will contain the results
of the query. After we have that in place we can update the div's innerHTML
with the information returned by ajax-example.php. Remember that this
result is stored inside ajaxRequest.responseText.
order.html HTML/Javascript Code:
<html>
<body>
<script language="javascript" type="text/javascript">
<!--
//Browser Support Code
function ajaxFunction(){
var ajaxRequest; // The variable that makes Ajax possible!
try{
// Opera 8.0+, Firefox, Safari
ajaxRequest = new XMLHttpRequest();
} catch (e){
// Internet Explorer Browsers
try{
ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try{
ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e){
// Something went wrong
alert("Your browser broke!");
return false;
}
}
}
// Create a function that will receive data sent from the server
ajaxRequest.onreadystatechange = function(){
if(ajaxRequest.readyState == 4){
var ajaxDisplay = document.getElementById('ajaxDiv');
ajaxDisplay.innerHTML = ajaxRequest.responseText;
}
}
var age = document.getElementById('age').value;
var wpm = document.getElementById('wpm').value;
var sex = document.getElementById('sex').value;
var queryString = "?age=" + age + "&wpm=" + wpm + "&sex=" + sex;
ajaxRequest.open("GET", "ajax-example.php" + queryString, true);
ajaxRequest.send(null);
}
//-->
</script>
<form name='myForm'>
Max Age: <input type='text' id='age' /> <br />
Max WPM: <input type='text' id='wpm' />
<br />
Sex: <select id='sex'>
<option value='m'>m</option>
<option value='f'>f</option>
</select>
<input type='button' onclick='ajaxFunction()' value='Query MySQL' />
</form>
<div id='ajaxDiv'>Your result will display here</div>
</body>
</html>
Quick Ajax Recap
So far we have created a new MySQL table, written a new PHP script and updated
order.html twice. If you have followed the directions in the Ajax MySQL lesson
and created the MySQL table ajax_example and ajax-example.php script then the updated order.html page will be functional.
Ajax Javascript Lessons
If you want to update a non form element, be sure to use the innerHTML
attribute that is associated with all HTML elements. In our case we are updating
a div every time a query is sent off. Also, remember that you can
easily access an HTML element by giving it an id and using Javascript's document.getElementById
function.
If you have successfully completed this advanced Ajax lesson then you know how to use
MySQL, PHP, HTML, and Javascript in tandem to write Ajax applications.
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