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An Introduction to Ajax Programming
- 1. An Introduction to Ajax Programming Dr. Harry Chen CMSC 491S/691S March 5, 2008
- 2. Agenda What’s Ajax?(revisit) JavaScript in 10 minutes DOM and XMLHttpRequest Programming Ajax with Mochikit Ajax Pitfalls Ajax in gnizr
- 3. Ajax A synchronous J avaScript A nd X ML The idea is to enable interactive Web pages without requiring the browser to refresh. Browser JavaScript code Web Server “ Give me some data” “ Here, data” Modify the page content, without refreshing the page
- 4. Ajax vs. traditionHTTP paradigm In the tradition HTTP world Every request results in a new page loading Dynamic pages are created on the server-side Data, format and styling are done on the server In the Ajax world The result of an Ajax call may only change a small parts of an existing HTML page Server sets up the page structure, JavaScript code performs the content creation Data, format and styling are done via JavaScript (CSS and XHTML)
- 5. Ajax is a3-Legged Stool XHTML JavaScript CSS Ajax Adopted from Simon Wilson: http://www.slideshare.net/simon/how-to-make-ajax-work-for-you
- 6. JavaScript in 10minutes Examples adopted from http://www.w3schools.com/js/js_examples.asp
- 7. Say “hello world”What’s ‘document’?
- 8. Write into HTML<body/> ‘ document ’ is a predefined JavaScript variable that represents the entire HTML document. You can read from and write to the current document via this ‘ document ’ variable.
- 9. Loading JavaScript codeTwo ways to load your JS code Inline within the same HTML document From a separate file on the server e.g., Replace ‘xxx.js’ with http://path/to/myprogram.js
- 10.
- 11. Define Array andAssociative Array
- 12.
- 13. Assign Function toa Variable In JavaScript, you can assign function to a variable.
- 14. Additional Resource JavaScriptTutorial http://www.w3schools.com/js/ PPK on JavaScript http://www.quirksmode.org/ I love it!
- 15.
- 16. DOM Document ObjectModel All XHTML doc are XML doc DOM is a process-model for XML For reading and writing XML doc We can use DOM to manipulate XHTML
- 17.
- 18. An XML DOM(not XHTML) <bookstore> <book category=“c1”> <title lang=“en”>Everyday Italian</title> <author>Giada De Laurentiis</author> <year>2005</year> <price>30.00</price> </book> </bookstore>
- 19. HTML DOM Tree– an example
- 20. JavaScript DOM Browser’sJS engines provides predefine HTML DOM objects
- 21. ‘Document’ DOM Predefinedobjects come with predefined properties and methods http://www.w3schools.com/htmldom/dom_obj_document.asp Watch out for browser support!
- 22. DOM Manipulation Operationsfor manipulating DOM objects are similar in different programming langauges – e.g., Java, PHP and JavaScript. Tutorial http://www.w3schools.com/dom/default.asp
- 23. XMLHttpRequest Is aspecification (see W3C doc) Defines an API that provides scripted client functionality for transferring data between a client and a server Browser JavaScript code Web Server “ Give me some data” “ Here, data.” Modify the page content, without refreshing the page Done via XMLHttpRequest
- 24. Clarification Use XMLHttpRequestto send and receive data from servers via HTTP Data sent and received can be any text format, not just XML. Works over HTTP and HTTPS http://www.w3.org/TR/XMLHttpRequest/
- 25. Fetch XML Datafrom the Server http://www.w3.org/TR/XMLHttpRequest/
- 26. Send data usingXMLHttpRequest http://www.w3.org/TR/XMLHttpRequest/
- 27. Common Problems with DOM and XMLHttpRequest
- 28. XMLHttpRequest Cross-browser IssuesMost browsers support the standard implementation, but some provide extra support that others don’t. Firefox implements standard and more IE implements just the standard
- 29. XMLHttpRequest Creation Creatingan XMLHttpRequest object is done differently depending on the browser. Checks which browser the client is using! Crazy!
- 30. DOM Cross-browser issuesDOM API differs from browser to brower. Remember this chart?
- 31. Get Node Value– FF vs. IE
- 32. Additional Reading AJAX- Common Pitfalls http://grover.open2space.com/node/92
- 33. Ajax Programming withMochikit
- 34. JavaScript Libraries Tomake JavaScript developer more productive, many JS libraries have been created. MochiKit I prefer; light-weight and simple jQuery Yahoo! UI library Prototype Script.aculo.us
- 35. MochiKit A collectionAPI that simplify JavaScript programming “Makes JavaScript suck a bit less” http://www.mochikit.com
- 36. Load MochiKit AllAPI can be loaded from a single file <script type="text/javascript" src="MochiKit.js"></script>
- 37. What does MochiKitprovide? Ajax programmers look here!
- 38. Fetch JSON Datafrom the Server The location of the data. Instantiate a function for making the call. Define how we want to handle the “response”. Actually makes the call.
- 39. What we didn’tdo! We didn’t have to create the XMLHttpRequest object ourselves. Don’t have to worry about those cross-browser issues. We don’t have to deal with HTTP methods -- “PUT”, “GET” etc.
- 40. Additional Reading ReadingMochiKit’s doc for How to manipulate DOM How to change CSS style How to deal with asynchronous events How to enable Drag and Drop How to exploit JavaScript functional and OO programming
- 41.
- 42. Ajax Programming IssuesBreaking the back button Not giving immediate visual cues for clicking widgets “Did I click?”, “I thought I have clicked”
- 43. Data loading issuesLoading… Please wait… (after 3 secs) I’m still loading. Please wait… (after 5 secs) I’m still loading. Please wait.. (after 30 secs) User: forget you. I’m leaving.
- 44. JavaScript Code LoadingIssue Too much JavaScript code can slow down the performance the client browser. Only use JavaScript and Ajax when it is necessary. More code != Better program
- 45. Search Crawler IssueText content rendered by JavaScript is not accessible to search crawler. Empty page?
- 46. Accessibility Notall screenreaders are built to work with Ajax applications. http://www.sitepoint.com/article/ajax-screenreaders-work
- 47. Summary Ajax programmingcan make Web pages to be more interactive and responsive. XHTML, CSS and JavaScript are the key components Ajax Ajax uses XMLHttpRequest object to send and receive data Study Ajax Pitfalls can help you to build more effective Mashup and Web 2.0 apps.
- 48. Ajax Programming ingnizr