AJAX Workshop Karen A. Coombs University of Houston Libraries Jason A. Clark Montana State University Libraries What is AJAX? AJAX stands for Asynchronous Javascript and XML. However,not all AJAX apps involve XML. AJAX uses a combination of technologies including: XHTML, CSS, DOM; XML, XSLT, XMLHttp, JavaScript; and a server scripting language such as PHP or Coldfusion. AJAX was created because web developers needed a method for building more responsive and interactive applications. AJAX Components XHTML and CSS Ajax applies these familiar Web standards for styling the look and feel of a page and to markup those areas on a page that will be targeted for data updates. DOM (document object model) Ajax uses the DOM to manipulate dynamic page views for data and to walkthrough documents to “cherrypick” data. The DOM enables certain pieces of an Ajax page to be transformed and updated with data. XML, JSON (Javascript Object Notation), HTML, or plain text Ajax can use any of these standards to provide structure to the data it passes to and from a page. XMLHttpRequest object The heavy lifter for Ajax: It’s a javascript object embedded in most modern browsers that sets up data request/response pipelines between client and server. Javascript Lightweight programming language that Ajax uses for instructions to bind all of the components together. Why Use AJAX? • You want to make your applications more interactive • You want to incorporate data from external Web Services • You don’t want your users to have to download a pluginClient vs. Server Scripting • Client scripting o Web browser does all the work • Server Scripting o Web server does all the work • AJAX leverages both client and server side scripting How AJAX Works AJAX Web Interaction • What you don’t see • Data reload happens in the background • JavaScript queries the server to get the proper data without you knowing it • Page updates without a screen “reload” Potential Problems • Javascript MUST be enabled • Back button doesn’t always work • Pages can be difficult to bookmark • Search engines may not be able to index all portions of an AJAX site • Cross browser differences in how XML is dealt with Some AJAX examples • Gmail • Flickr • Rojo • Google Suggest • Tada Lists Basic AJAX Components • Server-side Component – Communicates with the database, or web service – Can be written in any server-side language (PHP, ASP, Coldfusion, etc) • Client-side Component – Written in Javascript, often uses XMLHttp – Accesses the server side page in the background Hidden Frame Method • Communication with server takes place in a frame that user can’t see • Back and Forward buttons still work • If something goes wrong user receives no notificationXMLHttp Method • Code is cleaner and easier to read • Able to determine if there is a failure • No browser history, Back and Forward buttons break Potential Uses for AJAX • Error checking in forms • AutoSuggest • Drag and Drop objects functionality • Move around on image or map so you can see different parts • Preload content you want to show later • Apply limits to search results and get new results quickly AJAX for Libraries • Browsing subject headings • “Pre-displaying” indexes and databases categories • Complex ILL or contact forms • Federated Search • OPAC and digital library interfaces AJAX - Library Use Cases • Phoenix Live OPAC - OCLC Research (http://phoenix.orhost.org) • Federated Search - Curtin University of Technology Library (Perth, Western Australia) (http://library.curtin.edu.au/cgi-bin/search/search.cgi?query=&submit=Search) • Guesstimate - Virginia Tech Libraries (http://addison.vt.edu) AJAX – Sample Applications • PageInsert - WorldCat Form (http://localhost/ajax/) • BrowseSearch - LOC Subject Headings (http://localhost/ajax/browseloc.php)Code Sample #1: WorldCat Form WorldCat XML file to provide content <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <content> <header>What is Open WorldCat?</header> <description>The Open WorldCat program makes records of library-owned materials in OCLC's WorldCat database available to Web users on popular Internet search, bibliographic and bookselling sites. Links to content in library collections—books, serials, digital images and many other formats—appear alongside links to traditional Web content.</description> <sourceDomain>worldcatlibraries.org</sourceDomain> <sourceUrl>http://worldcatlibraries.org/wcpa/isbn/0471777781</sourceUrl> </content> Explanation • Our source file • Various and sundry factoids about WorldCat, some associated urls • header and description element to populate the heading and description of the content • sourceDomain will give an action value to our WorldCat search form • sourceUrl element will provide a link to an Open Worldcat record Code Sample #2: WorldCat Form Web page for user interface and display … <div id="container"> <div id="main"><a name="mainContent"></a> <h1>Find it in a Library. Use Open WorldCat.</h1> <p><a onclick="createRequest('xml/worldcat.xml');" href="#show">+ Learn more about Open Worldcat</a></p> <div id="content"></div> </div> <!-- end main div --> </div> <!-- end container div --> … Explanation • XHTML form that gives action to our script • Notice the javascript “onclick” event handler on <p> tag • <div id=“content”> will be populated with script messages OR new html tags received via our Ajax requestsCode Sample #3: WorldCat Form Using the XMLHttpRequest Object //creates browser specific request using XmlHttpRequest Object function createRequest(url) { if(window.XMLHttpRequest) { request = new XMLHttpRequest(); } else if(window.ActiveXObject) { request = new ActiveXObject("MSXML2.XMLHTTP"); } else { alert("Please upgrade to a newer browser to use the full functionality of our site."); } makeRequest(url); } //sends request using GET HTTP method to grab external data function makeRequest(url) { request.onreadystatechange = parseData; request.open("GET", url, true); request.send(null); } Explanation • First part of our javascript • Creates the XMLHttpRequest • Using the if and else statements to check for Web browsers’ different implementations of XMLHttpRequest • Ends with makeRequest