Ajax and xml
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Ajax allows asynchronous communication between a browser and server to update parts of a web page without reloading the entire page. It uses a combination of technologies including JavaScript, HTML, CSS, XML, and HTTP. The XMLHttpRequest object is used to asynchronously send and receive data from a web server in the background without interfering with the display and behavior of the existing page. This allows for faster and more interactive web applications.
Ajax and xml
- 1. 1 6-Mar-15 Ajax Asynchronous JavaScript and XML Introduction Ajax (sometimes capitalized as AJAX) stands for Asynchronous JavaScript And XML Ajax is a technique for creating βbetter, faster, more responsive web applicationsβ Web applications with Ajax are supposed to replace all our traditional desktop applications These changes are so sweeping that the Ajax-enabled web is sometimes know as βWeb 2.0β Introduction How Ajax works 1. You do something with an HTML form in your browser 2. JavaScript on the HTML page sends an HTTP request to the server 3. The server responds with a small amount of data, rather than a complete web page 4. JavaScript uses this data to modify the page You donβt have to reload the whole page like previously!!!
- 2. 2 Underlying technologies JavaScript HTML CSS XML XML is often used for receiving data from the server Plain text can also be used, so XML is optional HTTP All these are open standards What is AJAX? AJAX: 1) Asynchronous communication with the server 2) Retreiving data from the server (text or XML) 3) Updating the web page 1+2 = XMLHTTPRequest 3= DOM XMLHTTPRequest : Get data in XML, JSON or text format using HTTP requests. For IE7, Mozilla, OpΓ©ra, Safari β¦, we use XMLHTTPRequest. For subsequent versions of IE, we use MicroSoft.XMLHTTP or Msxml2.XMLHTTP we should then test the browser version before instantiation. Starting from the browserβ¦ Your browser must allow JavaScript, or Ajax wonβt work Otherwise, thereβs nothing special required of the browser Your browser has some way of providing data to the serverβusually from an HTML form JavaScript has to handle events from the form, create an XMLHttpRequest object, and send it (via HTTP) to the server Nothing special is required of the serverβevery server can handle HTTP requests Despite the name, the XMLHttpRequest object does not require XML
- 3. 3 The XMLHttpRequest object JavaScript has to create an XMLHttpRequest object Depending on the browser, there are three ways of doing this For most browsers, just do var request = new XMLHttpRequest(); For some versions of Internet Explorer, do var request = new ActiveXObject("Microsoft.XMLHTTP"); For other versions of Internet Explorer, do var request = new ActiveXObject("Msxml2.XMLHTTP"); Getting the XMLHttpRequest object function getXMLHttpRequest { var request = false; try { request = new XMLHttpRequest(); } catch(err1) { try { var request = new ActiveXObject("Microsoft.XMLHTTP"); } catch(err2) { try { var request = new ActiveXObject("Msxml2.XMLHTTP"); } catch(err3) { request = false; } } } return request; } Getting the XMLHttpRequest object Preparing the XMLHttpRequest object Once you have an XMLHttpRequest object, you have to prepare it with the open method request.open(method, URL, asynchronous) The method is usually 'GET' or 'POST' The URL is where you are sending the data If using a 'GET', data is appended to the URL If using a 'POST', data is added in a later step If asynchronous is true, the browser does not wait for a response (this is what you usually want) request.open(method, URL) As above, with asynchronous defaulting to true
- 4. 4 Sending the XMLHttpRequest object Once the XMLHttpRequest object has been prepared, you have to send it request.send(null); This is the version you use with a GET request request.send(content); This is the version you use with a POST request The content has the same syntax as the suffix to a GET request POST requests are used less frequently than GET requests Example: request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded'); request.send('var1=' + value1 + '&var2=' + value2); On the server side The server gets a standard HTTP request The response is a standard HTTP response too Instead of returning a complete HTML page as a response, the server returns an arbitrary text string (possibly XML, possibly something else) Getting the response Ajax uses asynchronous callsβyou donβt wait for the response Instead, you have to handle an event request.onreadystatechange = someFunction; This is a function assignment, not a function call When the function is called, it will be called with no parameters function someFunction() { if(request.readyState == 4){ var response = request.responseText; // Do something with the response } } To be safe, set up the handler before you call the send function Displaying the response http_request.onreadystatechange = function() { alertContents(http_request); }; http_request.open('GET', url, true); http_request.send(null); function alertContents(http_request) { if (http_request.readyState == 4) { /* 4 means got the response */ if (http_request.status == 200) { alert(http_request.responseText); } else { alert('There was a problem with the request.'); } } }
- 5. 5 The readyState property The readyState property defines the current state of the XMLHttpRequest object. Here are the possible values for the readyState property: readyState=0 after you have created the XMLHttpRequest object, but before you have called the open() method. readyState=1 after you have called the open() method, but before you have called send(). readyState=2 after you have called send(). readyState=3 after the browser has established a communication with the server, but before the server has completed the response. readyState=4 after the request has been completed, and the response data have been completely received from the server. Not all browsers use all states Usually you are only interested in state 4 http://www.w3schools.com/ajax/ajax_xmlhttprequest.asp Doing it with XML Hereβs an XML file named test.xml: <?xml version="1.0" ?> <root> I'm a test. </root> Then in alertContents() from the previous slide, we need to replace the line alert(http_request.responseText); with: var xmldoc = http_request.responseXML; var root_node = xmldoc.getElementsByTagName('root').item(0); alert(root_node.firstChild.data); http://developer.mozilla.org/en/docs/AJAX:Getting_Started innerHTML innerHTML is a non-W3C DOM property that gets or sets the text between start and end tags of an HTML element When the innerHTML property is set, the given string completely replaces the existing content of the object If the string contains HTML tags, the string is parsed and formatted as it is placed into the document Syntax: var markup = element.innerHTML; element.innerHTML = markup; Example: document.getElementById(someId).innerHTML = response; Summary Create an XMLHttpRequest object (call it request) Build a suitable URL, with ?var=value suffix request.open('GET', URL) request.onreadystatechange = handlerMethod; request.send(null); function alertContents() { if (request.readyState == 4) { // do stuff } } }