1 JavaScript & AJAX CS 236607, Spring 2008
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JavaScript & AJAX
CS 236607, Spring 2008
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JavaScript
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Overview JavaScript is a scripting language most often
used for client-side web development, and best known for this use in websites (as client-side JavaScript).
JavaScript is essentially unrelated to the Java programming language, though it copies many Java names and naming conventions.
JavaScript is used in many Web pages to add functionality, validate forms, detect browsers, and much more.
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JavaScript by Examples
We will look at some JavaScript examples…
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HelloWorld.html<html><body>
<script type="text/javascript">document.write(“<h1>Hello
World!</h1>");</script>
</body></html> DOM treatment of the
page
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DocumentURL.html<html><body>The URL of this document is:
<script type="text/javascript">document.write(document.URL);
</script>
</body>
</html>
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More Examples
Count the number of images in a document What are the coordinates of the cursor?
Notice events are thrown (events-driven)
Form Validation<html><head>
<script type="text/javascript">function validate() …(next slide)</script>
</head>
<body><form action="tryjs_submitpage.htm" onsubmit="return validate()">Name (max 10 chararcters): <input type="text" id="fname"
size="20"><br />Age (from 1 to 100): <input type="text" id="age" size="20"><br />E-mail: <input type="text" id="email" size="20"><br /><br/><input type="submit" value="Submit"> </form>
</body></html>
Form Validation (Cont.)<script type="text/javascript">function validate(){ var at=document.getElementById("email").value.indexOf("@"); var age=document.getElementById("age").value; var fname=document.getElementById("fname").value; submitOK="true";
if (fname.length>10){alert("The name must be less than 10 characters");submitOK="false"; }
if (isNaN(age)||age<1||age>100) {alert("The age must be a number between 1 and 100");submitOK="false"; }
if (at==-1) {alert("Not a valid e-mail!");submitOK="false"; }
if (submitOK=="false") {return false; }
}</script>
DOM Objects
JavaScript Function
Object Property
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AJAX
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Where Were We Before AJAX?
Static pages give the illusion of interactivity through standard form submissions.
Form submissions result in full page loads.
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So, What’s The Problem? Many actions only manipulate small portions of the
page but the entire page must be reloaded. Server responses contain the entire page content
rather than just the portion being updated. Loading entire pages typically results in several
additional HTTP requests for images, style sheets, scripts, and any other content that may be on the page.
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AJAX - Asynchronous JavaScript and XML A group of interrelated web development
techniques used on the client-side to create interactive web applications / rich Internet applications.
With Ajax, web applications can retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page.
Thus, the Web page can communicate with the server without refreshing the whole page.
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Real-Life Examples of AJAX Apps Google maps
http://maps.google.com/ Goolgle Suggest (Now integrated in Google’s
homepage) http://www.google.com/webhp?complete=1&hl=en
Yahoo Maps http://maps.yahoo.com/
Many more…
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AJAX Components JavaScript
DOM XMLHttpRequest object (XHR) XML
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Ajax Fundamentals
Ajax uses a three-step process:1. Request a URL by the JavaScript code – client side.
2. Handle the URL on the server and write to the response – server side.
3. After the response is complete, integrate the response into the DOM (Document Object Model) – client side.
In an Ajax request we don't refresh the entire page; instead, we update only part of the page.
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The Server sideDid we reduce the load on the server? Ajax newcomers sometimes mistakenly believe
that Ajax, because it provides a more responsive user interface, reduces server-side traffic.
In fact, Ajax applications typically have more server-side traffic because each Ajax request involves a trip to the server. Because those requests are asynchronous, however,
Ajax creates the perception of a more responsive UI, though it typically does not reduce the load on the server.
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So, How Does It Work? JavaScript is used to:
Create and control instances of the XMLHttpRequest (XHR) object.
Provide handlers for responses. Manipulate the DOM.
The XMLHttpRequest object: Allows scripts to perform HTTP client functionality. Supports GET and POST operations.
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Launching HTTP Requests
Typically, 3 steps are required:
1.1. Construct and configure an XMLHttpRequest object
2.2. Launch the request
3.3. Process the response
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Constructing an XMLHttpRequest
For Mozilla:
For Microsoft Explorer:
var request = new XMLHttpRequest();
var request = new ActiveXObject("Microsoft.XMLHTTP");
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Configuring an XMLHttpRequest
request.open("method","URL",false)
request.setRequestHeader("header","value")
• method is 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
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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")
The XHR Object
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To be continued…
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