Ajax a synchronous j avascript a nd x ml
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AJAX A synchronous J avaScript a nd X ML PowerPoint PPT Presentation


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AJAX A synchronous J avaScript a nd X ML. AJAX. An interface that allows for the HTTP communication without page refreshment Web pages are loaded into an object within the script (e.g., JavaScript) execution and integrated with the page content

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AJAX A synchronous J avaScript a nd X ML

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AJAXAsynchronous JavaScript and XML


AJAX

  • An interface that allows for the HTTP communication without page refreshment

  • Web pages are loaded into an object within the script (e.g., JavaScript) execution and integrated with the page content

  • Thus, the Web page can communicate with the server without refreshing the whole page


An Example


Launching HTTP Requests

Typically, 3 steps are required:

1.Construct and configure an XMLHttpRequest object

2.Launch the request

3.Process the response


Constructing an XMLHttpRequest

For Mozilla (+IE7.0):

For Microsoft Internet Explorer (<7.0):

var request = newXMLHttpRequest();

var request = new ActiveXObject("Microsoft.XMLHTTP");


Configuring an XMLHttpRequest

request.open("method","URL",false)

  • methodis GET, POST, etc.

  • URL must be in the domain of the current (or a relative URL), for security reasons

  • The false will be discussed later

request.setRequestHeader("header","value")


Launching the Request

request.send(content)

  • content is the posted in a POST request

  • content can be "null" or empty


Reading the Response

request.responseText

  • The response as flat text

request.responseXML

  • The response as a (DOM) Document object

  • Available if response Content-Type is text/XML

request.status

request.statusText

request.getAllResponseHeaders()

request.getResponseHeader("header")


An Example

<html>

<head>

<title>Jokes</title>

<script type="text/javascript">

... 2 slides ahead ...

</script>

</head>


An Example (cont'd)

<bodyonload="init(); setJoke()">

<h1>Select a Joke:</h1>

<p><select onchange="setJoke(value)">

<optionvalue="1"selected="selected">Joke 1</option>

<optionvalue="2">Joke 2</option>

<optionvalue="3">Joke 3</option>

</select></p>

<divid="jokediv"></div>

</body>

</html>


<script type="text/javascript">

var jDiv;

function init(){ jDiv = document.getElementById("jokediv");}

function setJoke(value){

request =new XMLHttpRequest();

request.open("GET","joke"+value+".txt",false);

request.send(null);

if(request.status==200){jDiv.innerHTML=request.responseText;}

else{jDiv.innerHTML ="<i>Cannot load joke...</i>";}

}

</script>


Asynchronous Requests

  • Reading of a Web page can take a long time during which the browser is blocked

  • Solution: launch the request asynchronously

  • That is, the execution continues after send is called without waiting for it to complete

  • When the request is completed, a predefined function is called

request.open("method","URL",true)


XMLHttpRequest States

  • The XMLHttpRequest goes through several states:

  • In the request configuration, you can define a function to call upon state change:

0 not initialized

1 loading

2 loaded

3 interactive

4 complete

request.onreadystatechange = functionName


XMLHttpRequest States (cont)

  • Use request.readyState to get the current state of the request

  • Use request.abort() to stop the request


An Example

var request;

function setJoke(value){

request =new XMLHttpRequest();

request.open("GET","joke"+value+".txt",true);

request.onreadystatechange = updateJokeDiv;

request.send(null);

}


An Example (cont'd)

function updateJokeDiv() {

if(request.readyState<4) {

jokeDiv.innerHTML ="<i>Loading...</i>";

return; }

if(request.status==200) {

jokeDiv.innerHTML = request.responseText; }

else {

jokeDiv.innerHTML ="<i>Cannot load joke!</i>"; }

}


Integrating AJAX and XML using DOM

The next example shows how XML data can be parsed and added into the content of your page


XML+AJAX Example

<html>

<head><title>Country List</title>

<scripttype="text/javascript">…</script>

</head>

<bodyonload="init();loadCountries()">

<h1>Select a Continent:</h1>


XML+AJAX Example (cont'd)

<p><selectid="continenetList"onchange="loadCountries()">

<optionvalue="asia">Asia</option>

<optionvalue="africa">Africa</option>

<optionvalue="europe">Europe</option>

</select></p>

<p><selectsize="10"id="countryList"></select></p>

</body>

</html>


XML+AJAX Example (cont'd)

function init() {

continents = document.getElementById("continenetList");

countries = document.getElementById("countryList"); }

function loadCountries() {

var xmlURL ="countries-"+continents.value+".xml";

var request =new XMLHttpRequest();

request.onreadystatechange = updateCountries;

request.open("GET",xmlURL,true);

request.send(null); }


XML+AJAX Example (cont'd)

function updateCountries() {

if(request.readyState==4) {

while(countries.length>0){countries.remove(0);}

if(request.status==200) {

var names =

request.responseXML.getElementsByTagName("name");

for(var i=0; i<names.length; ++i) {

option = document.createElement("option");

option.text=option.value=names[i].firstChild.nodeValue;

countries.appendChild(option);} }}}


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