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CSC 112 Intro to Computer Programming in JavaScript Spring 2005

CSC 112 Intro to Computer Programming in JavaScript Spring 2005. Internet and WWW. Internet and WWW are not the same – Internet includes email and other things Internet is the computers and the means by which they physically connect to each other.

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CSC 112 Intro to Computer Programming in JavaScript Spring 2005

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  1. CSC 112 Intro to ComputerProgramming in JavaScript Spring 2005

  2. Internet and WWW • Internet and WWW are not the same – Internet includes email and other things • Internet is the computers and the means by which they physically connect to each other. • World Wide Web is the logical means of accessing the files on these computers, primarily as web pages.

  3. Using the World Wide Web • Browsers Netscape Navigator Internet Explorer • Plug-ins Java Macromedia Flash Acrobat Reader … • Search Engines Yahoo and many others

  4. Internet Protocols • TCP/IP – Transmission Control Protocol / Internet Protocol • FTP – File Transfer Protocol • http – Hypertext Transfer Protocol • telnet – for remote login to other computers, with local computer as dumb terminal

  5. IP Addresses • Example – 123.45.67.89 • For specific computers on the Internet • Information is passed between them in packets • A named address (next slide) is converted to an IP address by a Domain Name Server (DNS)

  6. Named AddressesURL’s – Uniform Resource Locators http://www.music.sony.com/Music/index.html http is the protocol com is the domain – others are edu, org, gov, … www. music.sony.com is the server computer Music is the folder on the server computer index.html is the file in the Music folder

  7. Hypertext Markup Language • Describes with tags how web page should be formatted for display by browser • Container tags, thus <BODY> and </BODY> • Non container tags, thus <BR> or <HR> • Tags must be properly nested

  8. Basic Skeleton of an HTML Page <HTML> <HEAD> <TITLE> … </TITLE> </HEAD> <BODY> … </BODY> </HTML>

  9. For an unordered list <UL> <LI> <LI> … </UL> For an ordered list <OL> <LI> <LI> … </OL> Tags for Lists

  10. Attributes of HTML Tags • Describe how to accomplish a result • Attributes may or may not have values, as in <P ALIGN=left> …. </P> • BODY attributes include colors for links and for background • FONT attributes include color and size

  11. Hypertext Links • <A HREF=“some URL“> anchor text </A> (Absolute or relative URL’s) • <A HREF=“#fragment identifier”> anchor text </A> • <A NAME=“a named anchor”> </A>

  12. Images in Web Pages • Images appear when page is loaded, with <IMG SRC=“URL for image file”> • Image files for web pages are of type GIF or JPG • Image files are loaded via links, with <A HREF=“URL for image file”> some text </A>

  13. Programming • The Client-Server Model • Compiling versus Interpreting • Embedding JavaScript code in a web page • The Syntax or grammar of a P.L. (programming language) • Variables – numbers and strings and booleans • Operators – arithmetic and comparison • Concatenating strings with the overloaded + operator • Expressions – modifying precedence with parentheses • Statements – the assignment operator, the terminal semicolon

  14. Translating a Program to ML • Assembler Language (AL) • High Level Languages (HLL’s) Interpreting – Translate and execute on the fly Compiling – Translate source program to object program, then execute it, retaining translation for subsequent execution

  15. JavaScript Objects Thus, var foo = new Object() Objects may contain primitives of type number, string, or boolean other objects ! methods, or functions Thus, function foobar (){ statement; statement; … }

  16. Creating Forms with HTML <FORM … > <INPUT TYPE=text …> <INPUT TYPE=button …> <INPUT TYPE=reset …> <INPUT TYPE=checkbox …> <INPUT TYPE=radio …> <SELECT …> <OPTION …> <OPTION …> … </SELECT> <TEXTAREA …> </TEXTAREA> </FORM>

  17. Processing Forms with JavaScript Events, such as onclick and onchange Functions as event handlers Local variables in functions Converting strings to numbers with parseFloat() Arrays, as with var numbers = new Array() The elements array, automatically, for all of the items in the form selectedIndex for pull-down menus

  18. Arrays • The array is a special kind of object var foo = new Array ( ); where the items in foo are indexed by integer values, thus foo[1], foo[j], foo[2*k+3]… • If the first index value is 0, it is a standard array, as with elements[ ] and options[ ] • A property of an array is its size, as with foo.length

  19. Basic Tags for Tables <TABLE> <TR> <TD> <TD> … <TR> <TD> <TD> … </TABLE>

  20. Attributes of TableTags • <TABLE> … </TABLE> ALIGN, BGCOLOR, BORDER, CELLPADDING, CELLSPACING, HEIGHT, WIDTH • <TR> … </TR> ALIGN, VALIGN, BGCOLOR • <TD> … </TD> ALIGN, VALIGN, BGCOLOR, COLSPAN, ROWSPAN

  21. Control Structures • Sequential Processing do A, then B, then C, … • Conditional Processing (branching or selection) if A is true, then do B, else do C • Iterative Processing (looping or repetition) while A is true, do B {and test A again}

  22. Conditional Processing Comparison operators Boolean variables Logical operators for and, or, not if (boolean condition) { statement; statement; … } else { statement; statement; … }

  23. Iterative Processing • Must have three components - Initialize the loop control variable (lcv) • Test the lcv for termination • Update the lcv to next value • Thus, we have the for statement for (j = 0 ; j < 10 ; j += 1) { statement; statement; } • We also have the while statement j = 0; while (j < 10) { statement; j += 1; }

  24. Understanding Iteration • Word Problems To compute the number of days in the years 1950-2000 days = 0; for (years = 1950 ; years <= 2000 ; years++) if (years % 4 == 0) days += 366; else days += 365; • Tracing Iteration for (j = 1 ; j <= 3 ; j++) for (k = 0 ; k < j ; k++) document.write (j + “ ” + k + “<BR>”);

  25. Functions • Function definition (in the HTML head), thus function foobar (a, b, c) { statement; statement; } where a,b,c are formal parameters. • Function invocation or function call, thus foobar(5, j, “Hello”); where the values in parentheses are actual parameters; when foobar is called, a=5, b=j, and c=“Hello”

  26. Cookies • Name - Value pairs are just text strings! • When server responds to client request, it sends cookie to be stored on client. • When browser sends request to server, it retrieves cookie (if present) for server. • The GOOD for customizing user interface to server for implementing shopping carts • The BAD without user knowledge or consent contribute to junk mail and spamming • JS code to SetCookie(), GetCookie(), getCookieVal(), DeleteCookie()

  27. Sources of Errors • Typing errors • Syntax errors – incorrect grammar syntax is how a message is given • Logical errors – incorrect semantics semantics is the meaning • Poor algorithms • Bad input values – GIGO • Incorrect specification of the problem

  28. Computer Ethical Issues • Privacy versus security • Spamming • Email usage • Hacking • Ownership and piracy …

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