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Facebook Cookbook
book

Facebook Cookbook

by Jay Goldman
October 2008
Intermediate to advanced content levelIntermediate to advanced
434 pages
12h 7m
English
O'Reilly Media, Inc.
Content preview from Facebook Cookbook

Retrieving Data via Ajax

Problem

I want to do a call and/or response to my server without causing the current page to refresh. For example, I might want to dynamically populate some content, or update a section of my page, or maybe check to see whether some text entered into a field is valid.

Solution

Ajax can be used for such a wide variety of uses that it would require a whole other book to run down all the various permutations and combinations (conveniently, you can pick up any number of O’Reilly books on the topic, including Understanding AJAX: Using JavaScript to Create Rich Internet Applications and Ajax for Web Developers). As a simple example, we’re going to use a text field in which users would enter the username they’d like to use, and then we’ll check on the fly to see whether it’s available. You’ll need a text input on your Canvas page:

<div id="registration">
    <div id="usernameFields">
        <label for="username">Username:</label>
        <input type="text" id="username" onchange="checkUsername(this);" />
        <span id="usernameAvailable"></span>
    </div>
</div>

The JavaScript for checkUsername() is surprisingly simple because of the Ajax object provided by Facebook Platform, which really makes your life easy:

function checkUsername(usernameField){ if(usernameField.getValue() == ''){ document.getElementById('usernameAvailable').setTextValue(''); return; } var encodedUsername = escape(usernameField.getValue()); var checkUsername = new Ajax(); checkUsername.responseType = Ajax.JSON; checkUsername.ondone ...
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Publisher Resources

ISBN: 9780596156695Errata