1 JavaScript & AJAX CS , Winter 2007/8

2 JavaScript

3 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.

4 JavaScript by Examples We will look at some JavaScript examples…

5 Hello World document.write(“ Hello World! "); DOM treatment of the page

6 Document URL The URL of this document is: document.write(document.URL);

7 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 function validate() …(next slide) Name (max 10 chararcters): Age (from 1 to 100):

Form Validation (Cont.) function validate() { var 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 100) { alert("The age must be a number between 1 and 100"); submitOK="false"; } if (at==-1) { alert("Not a valid !"); submitOK="false"; } if (submitOK=="false") { return false; } } DOM Objects JavaScript Function Object Property

10 AJAX

11 Where Were We Before AJAX? Static pages give the illusion of interactivity through standard form submissions. Form submissions result in full page loads.

12 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.

13 AJAX - Asynchronous JavaScript and XML 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.

14 Real-Life Examples of AJAX Apps Google maps  Goolgle Suggest  Gmail  Yahoo Maps (new)  Many more…

15 AJAX Components JavaScript  DOM XMLHttpRequest object ( XHR ) XML

16 Ajax Fundamentals Ajax uses a three-step process: 1.Request a URL from JavaScript code on the client. 2.Handle the URL on the server and write to the response. 3.After the response is complete, integrate the response into the DOM (Document Object Model).  In an Ajax request we don't refresh the entire page; instead, we update only part of the page.

17 The Server side Did 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.

18 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.

19 Launching HTTP Requests Typically, 3 steps are required: Construct and configure an XMLHttpRequest object Launch the request Process the response

20 Constructing an XMLHttpRequest For Mozilla: For Microsoft Explorer: var request = new XMLHttpRequest(); var request = new ActiveXObject("Microsoft.XMLHTTP");

21 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

22 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.statusrequest.statusText request.getAllResponseHeaders() request.getResponseHeader("header")

24 Jokes... 2 slides ahead... An Example

Select a Joke: Joke 1 Joke 2 Joke 3 An Example (Cont.)

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 = " Cannot load joke... ";} } What if we didn’t get yet the response in this stage?

27 Example (Cont.) Our examples use “false" in the third parameter of open().  This parameter specifies whether the request should be handled asynchronously. True means that the script continues to run after the send() method, without waiting for a response from the server. Let’s see how it works, and how it is saved on the Tomcat server.

28 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)

29 XMLHttpRequest States The XMLHttpRequest goes through several states: In the request configuration, you can define a function to call upon state change: 0 0 not initialized 1 1 loading 2 2 loaded 3 3 interactive 4 4 complete request.onreadystatechange = functionName

30 XMLHttpRequest States (Cont.) Use request.readyState to get the current state of the request Use request.abort() to stop the request

31 var request; function setJoke(value) { request = new XMLHttpRequest(); request.open("GET","joke"+value+".txt",true); request.onreadystatechange = updateJokeDiv; request.send(null); } Asynchronous Example

function updateJokeDiv() { if(request.readyState<4) { jokeDiv.innerHTML = " Loading... "; return; } if(request.status==200) { jokeDiv.innerHTML = request.responseText; } else { jokeDiv.innerHTML = " Cannot load joke! "; } } An Example (Cont.)

33 Integrating AJAX and XML using DOM The next example shows how XML data can be parsed and added into the content of your page

34 Country List … Select a Continent: XML+AJAX Example

Asia Africa Europe XML+AJAX Example (Cont.)

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.)

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);} }}} XML+AJAX Example (Cont.)

38 JavaScript Libraries To reduce the amount of JavaScript code you need to write for Ajax requests, and to make sure that those requests succeed across multiple browsers, one better use a JavaScript library that neatly encapsulates those details and sharp edges in convenient JavaScript objects. The Prototype Library is one option. The Prototype Library

39 Resources DaveFancher.com Hebrew University Course javapassion.com W3 Schools Wikipedia Core JavaServer Faces(2nd Edition) / David Geary, Cay S. Horstmann