AJAX and REST

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What is AJAX? It’s an acronym for Asynchronous

JavaScript and XML Although requests need not be asynchronous

It’s not really a single technology but several HTML / CSS / DOM / XML

It’s used to dynamically update Web pages or at least parts of them

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What is AJAX? It uses the HTTPRequest and HTTPResponse objects to Make a server request from client

JavaScript And process the server-side response

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AJAX (model)

From W3Schools.com

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AJAX Frameworks Most vendors have their own AJAX

abstraction layers ASP has a script manager and an AJAX

toolkit It’s a layer on top of AJAX

There are several for PHP Phery, CJAX, Quicknet

There are frameworks for Python, Perl, Ruby and others

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RestFull APIs These are generally available API that

accept and execute AJAX requests Yahoo has YQL

SQL-like queries are built into the URL (GET request)

I’ll show this in class

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RestFull APIS Google has a number of APIs

These use JSON typically JSON is an alternative to moving the

responses around as XML

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AJAX (The Mechanics) The XMLHttpRequest object is used to create

a request The request gets configured with the open

method The request gets sent with the send method The responseText and responseXML

properties store the returned information Use the onreadystatechange event for

async requests

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AJAX XMLHttpRequest The following creates the request

var req = new XMLHttpRequest(); The open method define the type of request

The first argument contains the method to use (GET or POST)

The second argument contains the URL The third argument contains true

(asynchronous) or false (synchronous) The send method sends the request to the

server

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AJAX XMLHttpRequest (Example) Create open and send a synchronous

request

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AJAX Response (Synchronous) When the request completes, we get at

the response through the following properties of the XMLHttpRequest object responseText – gets the response data as

a string responseXML gets the response data as

XML, which we can then parse using the DOM

This is the same DOM we talked about

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AJAX Response (Synchronous)

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AJAX Response (Asynchronous) The onreadystatechanged event fires as

the request progresses Initialize Loading Loaded Interactive Completed

Status and status contain the result status information 404 – not found / 200 success

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AJAX Response (Asynchronous)

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AJAX (jQuery) As usual, jQuery makes the process

simple

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A Few Words about XML It’s the extensible markup language

Data is frequently stored and transported as XML

It looks like XHTML 5 Tags, attributes and elements Nesting concepts are the same

However the tag and attribute names can be any valid name

.NET knows about them

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A Few Words about XML Sample XML document

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REST Acronym for Representational State

Transfer REST (restful Web services) is a way of

exchanging HTTP requests and responses between client and server

It’s an alternative to Web Services and SOAP

It’s an alternative to Remote Procedure Calls (RPC)

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REST For read requests we

Send all data to the server via a URL and GET request

URLs are a logical location, rather than a physical resource

Data is typically returned as XML It’s not a standard but a way of doing

things An architecture of style YQL is restful

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A Few Words about YQL Yahoo Query Language Implemented as a Web service, they

maintain a number of tables Finance Geography and many more

http://developer.yahoo.com/yql/guide/yql-opentables-chapter.html#

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AJAX (References) http://w3schools.com/ajax/default.asp http://msdn.microsoft.com/en-us/

library/bb924552.aspxhttp://developer.yahoo.com/yql/

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HTML 5 http://www.ibm.com/developerworks/

library/x-html5/