1. JavaScript: Control Structures September 27, 2005 Slides modified from Internet & World Wide Web: How to Program. 2004 (3rd) edition. By Deitel, Deitel, and Goldberg. Published by Prentice Hall. ISBN 0-13-145091-3

2. Chapter 7 - JavaScript: Introduction to Scripting Outline 7.1 Introduction 7.2 Simple Program: Printing a Line of Text in a Web Page 7.3 Obtaining User Input with prompt Dialogs 7.3.1Dynamic Welcome Page 7.3.2Adding Integers 7.4 Memory Concepts 7.5 Arithmetic 7.6 Decision Making: Equality and Relational Operators 7.7 Web Resources

3. Objectives In this lesson, you will learn: –To be able to write simple JavaScript programs. –To be able to use input and output statements. –To understand basic memory concepts. –To be able to use arithmetic operators. –To understand the precedence of arithmetic operators. –To be able to write decision-making statements. –To be able to use relational and equality operators.

4. Introduction to JavaScripting

5. 7.1 Introduction JavaScript scripting language –Enhances functionality and appearance –Client-side scripting Makes pages more dynamic and interactive –Foundation for complex server-side scripting –Program development –Program control

6. What can JavaScript programs do? From http://www.javascripter.net/faq/javascri.htmhttp://www.javascripter.net/faq/javascri.htm Giving the user more control over the browser Detecting the user's browser, OS, screen size, etc. Performing simple computations on the client side Validating the user's input Handling dates and time Generating HTML pages on-the-fly without accessing the Web server.

7. What can’t JavaScript programs do? From http://www.javascripter.net/faq/javascr2.htmhttp://www.javascripter.net/faq/javascr2.htm Use printers or other devices on the user's system or the client-side LAN Directly access files on the user's system or the client-side LAN ; the only exception is the access to the browser's cookie files. Directly access files on the Web server. Implement multiprocessing or multithreading.

8. Programming context Interpreted language Web browser as the interpreter Client-side only –Compatibility depends on browser version But virtually every browser supports JavaScript Follow ECMAScript standard!ECMAScript –Security issues You cannot access the client’s system beyond their web browser –Thus, no file access or direct printing

9. Notes on compatibility Browser versions –80-90% of people user Internet Explorer Of which 99% use IE 6 or IE 5 –10-15% use Gecko-based browsers Firefox, Netscape, Mozilla JavaScript and cookies –Only 85-90% have JavaScript enabled –Cookies usually enabled by default—I don’t have statistics for how many leave this on Screen resolutions –25% use 800x600 –70% use 1024x768 or higher Recommendations: –Test all pages with IE 5/6 and Firefox –Don’t assume that users have JavaScript or cookies enabled Your site should still be functional without client-side scripting or cookies –Design to be comfortably viewable with 800x600 resolution Sources –http://www.upsdell.com/BrowserNews/stat_trends.htmhttp://www.upsdell.com/BrowserNews/stat_trends.htm –http://www.w3schools.com/browsers/browsers_stats.asphttp://www.w3schools.com/browsers/browsers_stats.asp

10. Object orientation in JavaScript JavaScript is an object-oriented programming language –Based on objects with properties and methods JavaScript uses prototyping to replicate behaviour, rather than classification (classes) There are two types of variables: –Simple variables (also called “primitives”) –Objects

11. Objects in JavaScript An object is a complex type of variable that contains its own variables (properties), and has its own functions (methods) –Properties The variables of an object Can also be other objects –Methods The functions that belong to an object –e.g. document.bgColor, window.location JavaScript has a rich set of built-in objects –http://www.devguru.com/Technologies/ecmascript/quickref/js_objects.ht mlhttp://www.devguru.com/Technologies/ecmascript/quickref/js_objects.ht ml You can also define your own objects

12. How to specify JavaScript code Inline Code –Add dynamic functionality to an individual element Write JavaScript code directly in appropriate event attributes Embedded scripts –Embed JavaScript code in an XHTML document—either in the head or in the body x=3; y=9; document.writeln( x + y ); Inserting external scripts –Insert a file with “.js” extension that contains JavaScript code JavaScript libraries can be shared by multiple XHTML documents A note on CDATA – –Necessary for legal XML to ignore & and < symbols (which are common in scripts) –However, most browsers work fine without them –http://www.w3schools.com/xml/xml_cdata.asphttp://www.w3schools.com/xml/xml_cdata.asp –The textbook says to use But CDATA is proper XML syntax Comments should validate, but not guaranteed

13. First scripts

14. 7.2 Simple Program: Printing a Line of Text in a Web Page Inline scripting –Written in the of a document – tag Indicate that the text is part of a script type attribute –Specifies the type of file and the scripting language use writeln method –Write a line in the document Escape character ( \ ) –Indicates “special” character is used in the string alert method –Dialog box

15. welcome.html (1 of 1)

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19. Illegal characters in XHTML vs. JavaScript XHTML –HTML entities & < > Others: http://www.w3schools.com/tags/ref_entities.asphttp://www.w3schools.com/tags/ref_entities.asp JavaScript –Escape sequences \’ \” \n \t \\ Others: http://www.devguru.com/Technologies/ecmascript/quickref/escaped_characters.html http://www.devguru.com/Technologies/ecmascript/quickref/escaped_characters.html To convert between the two, use an XHTML  JavaScript converter –Google “HTML JavaScript converter” –Best that I’ve found: http://javascript.about.com/library/blscr02.htm

20. 7.2 Common escape sequences For full list, see http://www.devguru.com/Technologies/ecmascript/quickref/escaped_characters.html http://www.devguru.com/Technologies/ecmascript/quickref/escaped_characters.html

21. 7.3.1 Dynamic Welcome Page A script can adapt the content based on input from the user or other variables

22. welcome5.html (1 of 2)

23. 7.3.1 Dynamic Welcome Page Fig. 7.7Prompt dialog displayed by the window object’s prompt method. This is the prompt to the user. This is the default value that appears when the dialog opens. This is the text field in which the user types the value. When the user clicks OK, the value typed by the user is returned to the program as a string.

24. JavaScript data types In JavaScript, you can use the var statement to create a variable, but it is not required You do not declare any data type (loosely typed) –For scripting languages, data types are automatically determined –Automatically converts between values of different types JavaScript data types –Numbers Numbers are numbers, whether integer or floating point –Boolean values true or false –Strings “Anything within quotes” ‘Anything within quotes’ –Null "special key word denoting a null value" Means “no value” –From http://www.ryerson.ca/JavaScript/lectures/basicDataTypes/basicTypes.htmlhttp://www.ryerson.ca/JavaScript/lectures/basicDataTypes/basicTypes.html

25. 7.3.2 Adding Integers Prompt user for two integers and calculate the sum (Fig. 7.8) NaN (not a number) parseInt –Converts its string argument to an integer

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27. JavaScript native functions See http://www.devguru.com/Technologies/ecmascript/quickref/js_functions.html http://www.devguru.com/Technologies/ecmascript/quickref/js_functions.html parseInt() –Converts a string into an integer, if possible parseFloat () –Converts a string into a floating-point number, if possible string () –Converts any object into a string number () –Converts any object into a number, if possible isNAN () –true if the object is Not A Number escape() and unescape() –Converts and deconverts strings to “safe” characters

28. Operators in JavaScript http://www.devguru.com/Technologies/ecmascript/quickref/js_operators.html

29. 7.5 Arithmetic operators

30. 7.6 Decision Making: Equality and Relational Operators  

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33. 7.6 Decision Making: Equality and Relational Operators