Using Google`s Ajax Libraries API - Building a simple Ajax application using a local copy of the Prototype JavaScript library (
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Before I show you how to take advantage of Google’s API to work with a specific JavaScript library, I will build a simple Ajax program with the Prototype framework. I'm going to use a conventional approach, that is, I will build the program with a local copy of the framework.
Once you’ve grasped how this Ajax application works, I will demonstrate how to rebuild it by using Google’s API. In this way you’ll be able to spot the differences in both approaches.
Having clarified that point, it’s time to begin developing this sample Ajax program. In simple terms, the program will be tasked with reading the contents of a text file, naturally stored in the web server, which will be displayed on screen via the Ajax module that comes bundled with Prototype. Quite easy to grasp, right?
So, here’s the definition of a basic the text file, called “data.txt,” whose contents will be fetched with Ajax:
These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file. These are contents of sample file.
Indeed, the above text file is extremely simple to read, meaning that it’s time to start building the Ajax application that will be charged with retrieving its contents. Below I included the complete source code of this application. Here it is:
(definition for 'ajax_file_reader.htm' file)
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Reading file contents with Prototype library</title>
<style type="text/css">
body{
padding: 0;
margin: 0;
background: #fff;
}
h1{
font: bold 18pt Arial, Helvetica, sans-serif;
color: #000;
}
#filecontents{
width: 600px;
padding: 10px;
border: 1px solid #999;
font: normal 10pt Arial, Helvetica, sans-serif;
color: #000;
}
</style>
<script language="javascript" src="prototype-1.4.0.js"></script>
<script language="javascript">
// read file contents with Ajax
function readFileContents(){
// send http request
var ajaxobj=new Ajax.Request('read_file.php',{method: 'get',onComplete:
displayFileContents,onFailure: displayError});
}
// display file contents
function displayFileContents(requestObj){
$('filecontents').innerHTML=requestObj.responseText;
}
// display error message
function displayError(requestObj){
$('filecontents').innerHTML='Error reading file contents!';
}
// initialize file reading application
function initializeApplication(){
// attach handler to HTML button
Event.observe('btn','click',readFileContents);
}
// attach handler to window object
Event.observe(window,'load',initializeApplication,false);
</script>
</head>
<body>
<h1>Reading file contents with Prototype library</h1>
<p><input type="button" id="btn" value="Read File Now!" /></p>
<div id="filecontents"></div>
</body>
</html>
(definition for 'read_file.php' file)
<?php
if(!$contents=file_get_contents('data.txt')){
trigger_error('Error reading file contents',E_USER_ERROR);
}
echo $contents;
?>
Even if you’re not familiar with working with the Prototype JavaScript library, it’s pretty easy to see how the above Ajax application functions. It downloads a local copy of the library, and then fetches the content of the previous text file; finally, the application displays it on the browser via an Ajax-based HTTP request.
In addition, the script that actually reads the target file and sends the data back to the client is the one called “read_file.php,” whose signature is shown above as well.
To complement the previous explanation, here’s a screen shot that depicts quite clearly how this Ajax-driven programs works:
Well, at this point I've explained how to build a basic Ajax application by using a local copy of the Prototype framework. Next, I will reconstruct the application by means of the Google API.
To learn the full details of how this will be accomplished, please read the following section.
