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Web Developer Foundations: Using XHTML Chapter 12 Adding Interactivity to Your Web Pages 1 Learning Outcomes In this chapter, you will learn how to: Describe the features and common uses of JavaScript • Add JavaScript code to a web page Describe the features and common uses of Java Applets • Add a Java Applet to a web page Describe the features and common uses of DHTML • Add a DHTML effect to a web page Describe the features and common uses of CGI • Invoke CGI from a web page Describe the features and common uses of Macromedia Flash • Add a Flash Animation to a web page Find free Javascript, Java Applets, DHTML, CGI, and Flash resources on the Web Describe other technologies that can be used to add web page interactivity 2 What is JavaScript? Object-oriented scripting language. Used to work with the objects associated with a web page document --the window, the document, the elements such as forms, images, links, etc Originally developed by Netscape and called LiveScript Netscape collaborated with Sun Microsystems on modifications to the language and it was renamed JavaScript JavaScript is NOT Java 3 Common Uses of JavaScript Display a message box Select list navigation Edit and validate form information Create a new window with a specified size and screen position Image Rollovers Status Messages Display Current Date Calculations 4 Coding JavaScript JavaScript code can be added to a web page using two different techniques: Place Javascript code between <script> tags Place Javascript code as part of an event attached to an XHTML element 5 JavaScript Using <script> tags The script tag A container tag May be placed in either the header or the body section of a web page (see ex1.htm) <script language="JavaScript" type=”text/javascript”> <!- alert("Welcome to Our Site") // - -> </script> 6 JavaScript and Events Events are actions that the visitor to the web page can take such as clicking (onclick), (ex4.htm) placing the mouse on an element (onmouseover), (ex5.htm) removing the mouse from an element (onmouseout), (ex6.htm) loading the page (onload), (ex1a.htm) unloading the page (onunload), (ex1b.htm) etc. 7 JavaScript and Events JavaScript can be configured to perform actions when these and other events occur. The JavaScript code is added directly to the XHTML tag with the type of event as an attribute. The value of the event attribute will contain one or more JavaScript statements. 8 JavaScript Coding for Events The sample code below will display an alert box when the mouse is placed over a link. <a href=”home.htm” onmouseover=”alert(‘Click to go home’)”>Home</a> 9 JavaScript Debugging Check the syntax of the statements that you typed - pay very close attention to upper and lower case letters, spaces, and quotations. Verify that you have saved the page with your most recent changes. Verify that you are testing the most recent version of the page (refresh or reload the page) If you get an error message, Use the error messages that are displayed by the browser. Some web authoring tools such as Microsoft FrontPage and Macromedia Dreamweaver provide line numbers for the XHTML/JavaScript source code. Macromedia Dreamweaver has its own JavaScript debugger that will let you step through the code. 10 What is Java? Java is an Object Oriented Programming (OOP) language developed by Sun Microsystems. Java is not the same language as JavaScript. Java is more powerful and much more flexible than JavaScript. Java can be used to develop both stand-alone executable applications and applets that are invoked by web pages. 11 Java Applets Java applets (“.java” files) are compiled (translated from the English-like Java statements to an encoded form) and saved as “.class” files which contain byte code. The byte code is interpreted by the Java Virtual Machine (JVM) in the web browser. The JVM interprets the byte code into the proper machine language for the operating system. The applet is then executed and appears on the web page. 12 Common Uses of Java Applets Navigation Bars and Buttons Image Effects Text Effects Games Web and Business Applications See example: ex8.htm 13 Adding a Java Applet to a Web Page The applet tag A container tag Attributes: code, codebase, height, width, alt, id Works together with <parameter> tags Stand alone tags Attributes: • name, value The <parameter> tags used by an applet are determined by the developer who writes and distributes the applet 14 Sample Java Applet <applet code=“myapplet.class" height=“50" width=“500“ alt=“Java applet: displays a moving logo with company name”> <param name="bgColor" value="#FFFFFF" /> <param name=“txtColor" value="#0000CC” /> This Java applet displays a moving logo with the company name </applet> The sample applet is named myapplet.class and requires two parameters, bgColor and txtColor. 15 What is DHTML (Dynamic HTML)? A group of technologies work together to change a web page after it has been downloaded. These technologies allow the web page to respond to user actions. Technologies used in DHTML: Document Object Model (DOM) Cascading Style Sheets (CSS) Client-side Scripting 16 Document Object Model (DOM) The DOM defines every object and element on a web page. Its hierarchical structure can be used to access page elements and apply styles to page elements. A portion of the DOM is shown at the right. 17 More on DHTML Has a long learning curve because of the extent of the knowledge needed Implemented differently by major versions of the major browsers, Convergence between the DHTML implementations of Internet Explorer 5 It should become easier to write cross-browser DHTML in the future. to successfully combine the three technologies. Internet Explorer and Netscape. DHTML coded to work in Internet Explorer will often not work in Netscape. DHTML coded to work in Netscape 4.x will not work in Netscape 6. and Netscape 6 is better. 18 Common Uses of DHTML Hiding and showing text Navigation Image Effects See example: ex9.htm 19 Adding DHTML to a Web Page The code needed to add a DHTML effect to a web page will vary based on the desired effect – usually using a combination of CSS and JavaScript. The JavaScript tends to get complex because of the differences in the syntax required for different browser and browser versions. It is a good idea to become comfortable with CSS and JavaScript before tackling DHTML. 20 What is Macromedia Flash? Flash is a popular multimedia application developed by Macromedia. It is often used to create animation and multimedia effects on web pages (ex10.htm) Flash effects are saved in “.swf” files .swf files play as they download and give the perception of speedy display of complex graphic animations Flash requires a free browser plug-in, which is available for download from Macromedia 21 How to create Macromedia Flash? “.swf” files can be created in a number of applications including • Macromedia Flash, • Macromedia Fireworks, • Macromedia Dreamweaver, • Swish, • and Adobe LiveMotion 22 Common Uses of Macromedia Flash Navigation Splash Screen Entire Web Site 23 Adding Flash to a Web Page Both the <object> tag and the <embed> tag are used to place Flash media on a page Some versions of currently popular browsers such as Netscape support the <embed> tag and do not fully support the <object> tag. Use the <noembed> tag to contain a text description of the Flash media in order to provide for accessibility. 24 Flash General Sample <object … object attributes go here…. <param name="movie" …value attribute goes here… /> <param name="quality" …value attribute goes here… /> <param name="bgcolor" …value attribute goes here… /> <embed … object attributes go here…. /> <noembed> … a brief description of the Flash media can go here along with a link to alternate text content if appropriate… </noembed> </object> 25 Flash Detail Sample The following code places a Flash file called flashbutton.swf on a web page: <object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.ca b#version =4,0,2,0" width="147" height="34"> <param name="movie" value="flashbutton.swf" /> <param name="quality" value="high" /> <param name="bgcolor" value="#FFFFFF" /> <embed src="flashbutton.swf" quality="high" pluginspage="http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_ Version=ShockwaveFlash" type="application/x-shockwave-flash" width="147" height="34" bgcolor="#FFFFFF" /> <noembed>This is a Flash button that links to <a href=”http://macromedia.com”>Macromedia’s web site</a> </noembed> </object> 26 What is CGI? Common Gateway Interface A standard method for web pages to request special processing on the web server. Provides a protocol for a Web server to pass a Web page's request to a program or script stored on the server, receive a response from the program or script, and send that response to the web browser for display. CGI scripts/programs can be written in many languages, including Perl and C++. 27 Steps in Utilizing CGI Web page invokes CGI by a form post, action, hyperlink, etc... 1. Any form information is sent in the form of name=value pairs to the web sever. 2. CGI script on web server is executed 3. CGI script accesses requested database, file, or process 4. Web server returns web page with requested information or confirmation of action 28 Common Uses of CGI Search a database Place an order at an online store Send a web page to a friend Subscribe to a newsletter Any type of server-side file or e-mail processing is a candidate for CGI 29 Using CGI Invoke a CGI from an Anchor Tag <a href="http://terryfelke.com/cgi-bin/date.pl">Server Date and Time</a> Invoke a CGI from a Form When a web page visitor clicks the "Submit" button on a form, the form data is sent to the URL in the form tag's action attribute. This URL should be a CGI script or other server-side processing technique. <form method=“post” action=http://terryfelke.com/cgi-bin/order.pl”> Method Attribute • “get” is the default. This places the form information appended to the URL in the HTTP request sent to the web server. • “post” is preferred by W3C. This places the form information in the entity body of the HTTP request to the web server. 30 Summary of Interactive Technologies The purpose of this chapter was to introduce you to a number of technologies used to add interactivity to web pages. As you continue your studies, you may choose to specialize in one or more of these technologies. 31