1. JavaScript I ECT 270 Robin Burke

2. Outline Midterm answers JavaScript Programming Syntax Interacting with the browser Variables and data types Arrays Flow of control Function definitions Date object Final Project Homework #6

3. Midterm High = 100 (1) Low = 43 Avg = 78

4. Midterm answers

5. Why JavaScript? Web application round-trip expensive no way to do computation on the client side example: form validation Web pages static no way to allow users to interact with the page example: popup link menus What is needed client-side code

6. JavaScript Very little connection to Java marketing move by Netscape JavaScript is a scripting language for web clients interpreted untyped Dynamic HTML combination of JavaScript, CSS and DOM to create very flexible web page presentation

7. JavaScript history Introduced with Netscape 2.0 MS copied with JScript In 1998, ECMAScript became a standard proprietary names still used ECMA sets minimum standards

8. JavaScript Programming Easy to work with edit page view in browser no compilation / linking / libraries / etc Easy to get in trouble easy to skip documentation, proper coding practices Headaches browser compatibility browser-version compatibility

9. Best Practices Naming lower/upper for variable names e.g. "upperRight". Documentation Documentation of each significant variable Sparse documentation within the body of a function (usually on the right side of expressions) so as not to interfere with understanding the flow of control Style Careful delineation of the start and end of functions Alignment of expressions so that differences between similar expressions can easily be spotted Embedded output Format HTML so it closely corresponds with the actual appearance of the output Goal = Understandable code

10. Our Practice: PDL Write PDL first as comments program design language what the program should do in "application" terms, not code terms no variable names no operators Integrate PDL with code as it is written

11. Example PDL add the right margin to the block offset to find the horizontal position of the block Program h = marginR + offset; PDL find the highest and lowest scores on exam Program...

12. Our Practice: Iterative Development Working ≠ Finished When the program works, ask how could it be improved? what are the vectors of change? Dimensions of improvement readability / organization compactness cleanliness modularity / flexibility efficiency

13. Our Practice: In-class coding Programming is an interactive activity hard to teach in lecture setting We'll program our examples together

14. Debugging JavaScript Browser settings Internet Options.../Advanced Display a notification about every script error Disable script debugging

15. JavaScript and HTML Identifying script sections and But some browser can't / don't process Problem script becomes part of the page content Solution enclose script in HTML comments

16. JavaScript skeleton... HTML head content... <!—... code here executed on loading... //-->... page content... <!--... code here executed during page rendering... //-->... more page content...

17. JavaScript execution model Interpreted Code is executed as read Outside of SCRIPT elements HTML output as usual Inside SCRIPT elements JavaScript evaluated May or may not result in output to the page At the end of the page JavaScript program terminates but code may still be resident event handling

18. Basic syntax Statement end  ; a = a + 1; Grouping statements  { } if foo { bar; } Comments  // and /* */ // this is a comment JavaScript is case-sensitive

19. Objects JavaScript uses objects dot syntax to access fields and methods Methods document.write ("foo"); calls the method write on object document with argument "foo" Fields document.lastModified gets the date from the HTTP header

20. Interacting with the browser Built-in objects window methods and fields related to the browser document methods and fields related to a particular document displayed in the browser The point we manipulate the browser and its contents programmatically

21. window window.navigator an object describing the user's browser useful for code that depends on a particular browser version example: window.navigator.appName window.frames[] an array containing all of the frames in a framed document example: window.frame[0] window.status access to the contents of the status bar in the browser example: window.status window.history access to the browser's history list example: window.history.back()

22. window, cont'd opening new windows window.open creates a new browser window (pop-up) example: window.open ("www.cti.depaul.edu") window.alert() opens a dialog with a message example: window.alert ("The system has crashed.") window.confirm() opens a dialog that the user can OK or cancel returns true if OK example: window.confirm ("Proceed to erase hard disk?") window.prompt() opens a dialog that returns a value example:window.prompt("Enter user id:")

24. document document.images all the images in the document example: document.images[2] document.write / writeln methods for adding content to the document example: document.writeln ("foo"); document.forms all the forms in the document document.all all the HTML elements in the document

25. Elements We have access to the HTML elements in the document change attributes change contents

26. Examples Hello, world write text to the page write HTML to the page Browser info write browser appName and version to the page Pop-up use the alert and open methods

27. Variables and data types JavaScript data types numeric string boolean object reference like in Java ignore book viz. "null" Remember JavaScript is untyped no type declarations you have to keep track of what is stored where

28. Declaration Variables do not have to be declared using a variables makes it exist But, for this class all variables must be declared unlike Java, not types Declaration var foo;

29. Arrays Normally A fixed-size collection of identically typed data items distinguished by their indices JavaScript doesn't require X fixed size X identical types Example document.images[0]

30. Arrays cont'd Creating an array var a = new Array (); Accessing a[0] = 5; a[1] = "foo"; a[2] = 10; b = a[0] + a[2];

31. Example Image swap wait for alert, then swap images Image swap, with preloading Multi image swap

32. Control flow Standard options available Conditional Loops for while do

33. If statement The same as Java if test {... if part... } else {... else part... }

34. Example Conditional image display display second image if user answers "OK" to a confirmation

35. For loop Mostly the same as Java for (i = 0; i < 5; i++) {... repeated part... } Variant for object properties for (i in documents) {... repeated part... }

36. Example Slide show once-through Slide show recycling

37. Functions In Java you wrote functions associated with classes methods In JavaScript we won't be defining new classes we write functions with global scope can be called anywhere on the page next week we'll see how functions can be called from events functions can also simplify programs

38. Functions cont'd Syntax function name(parameter list) {... function code... } Placement best place is in the HEAD element recall skeleton must be before first invocation

39. Function cont'd Functions need not return a value different from VB If a function does return a value, use return value; Scope variables declared with var inside a function are local different from Java all variables in a method are local

40. Example slide show with functions

41. The Date object JavaScript has a built-in object classes for programmers to use The Date object used in the homework relevant for doing time and date computations days until Chirstmas in book contains both date and time

42. Date object, cont'd Constructor new Date (parameters) Parameters can be a single string new Date ("October 27, 2003"); a list of values new Date (2003, 9, 27); empty = current date and time new Date (); Internal representation count of milliseconds

43. Components of the date Accessors getYear() returns year getMonth () returns month getDay (), getHours(), getMinutes(), getSeconds() Calculations from millisecond representation

44. Using lastModified date document.lastModified returns a Date in String form not in JavaScript date form Must use the Date constructor new Date (document.lastModified)

45. Example Greetings How long ago modified?

46. Final Project Teams up to size 3 solo OK Tourism site you decide destination Presentation 11/24 in class demonstrate the site

47. Final Project cont'd Requirements 9 pages CSS navigation 1 dynamic effect Pages home page order form with validation slide show credits page 5 other pages

48. Final Project cont'd Rubric 15% presentation 20% design and layout 65% technical For an "A" all required elements visual appeal easy to use attractive design effort commensurate with team size

49. Final Project cont'd Do's plan ahead sketch on paper first start early and make steady progress Don'ts HTML editor "Borrowed" JavaScript Last minute rush

50. Homework #6 Case 1 Chapter 8 Meal of the day Zodiac page Use JavaScript prompts to gather date of birth Display zodiac sign