COP 3813 Intro to Internet Computing

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COP 3813Intro to Internet Computing

• Prof. Roy Levow
• Lecture 4
• JavaScript

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JavaScript

• JavaScript
• Object-oriented programming language
• Interpreted from source code
• Supported by most browsers
• Executed on client system in browser
• Program text output is treated as html and
  rendered by browser
• Includes extensive support for generating web
  page and window elements

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Variables and Assignment

• Variable names essentially as in C
• No type in declaration
• var name1, name2,
• Assignment operator

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Expressions

• Very similar to C
• Arithmetic Operators
• - / -- etc. as in C
• Comparison operators lt lt
• String concatenation with
• also converts other values to string if possible
• Output with
• document.writeln( str )
• Input with
• val window.prompt(msg)

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Basic Control Structures

• if (cond)
• stmt
• else // optional else part
• stmt
• // block
• while (cond)
• stmt
• for (init test incr) stmt

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Use on Web Page

• Generates code where script is executed in body
• Functions can go in head
• Wrap with
• ltscript type text/javascriptgt
• lt!--
• // code goes here
• --gt
• lt/scriptgt

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Examples

• Class Average 2 (fig. 8.9)
• Analysis (fig. 8.11)
• Interest Table (fig. 9.6)

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More Control Statements

• switch (choice)
• case val stmt
• break
• default // optional
• stmt
• do stmt while (cond)

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Examples

• Bullet lists with switch (fig. 9.7)
• Headings with do-while (fig. 9.9)

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Logical Values and Operators

• Logical Values are
• true false
• Usual logical operators
• !
• Short-circuit evaluation

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Defining Functions

• function fname(parm1, parm2, )
• //code
• return expr
• Notes
• No return type
• expr in return omitted if no return value

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Example

• Table of Random Numbers
• (fig. 10.4)
• Note use of functions from class Math
• Die Roll (fig. 10.5)
• Craps (fig. 10.6)

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Arrays

• Array is a class
• Declare array with
• var list new Array(size)
• Access with listindex
• Start with 0
• Can hold any type of value
• Deallocation is automatic when another value is
  assigned to variable
• list.length returns length

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Arrays Initialization

• In constructor
• new Array(red, green, blue)
• By array object
• x 1, 2, 3, 4
• Can have undefined values never assigned
• Example DieRoll, fig. 11.6

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Reference Parameters

• Arrays and objects are passed by reference so a
  change in the function changes the calling value
• Scalars are passed by value

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Two-dimensional Arrays

• Declare an Array for rows
• Then assign an Array to each element
• Does not enforce rectangular form
• Access with Arrayij

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Objects

• Similar to C
• Declared with new
• Math object has elements that are standard math
  functions
• Math.sin(x)

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Strings

• Class String supports character strings
• Constants are surrounded by
• Can use usual C \ escaped
• Has many methods for string manipulation
• Operator for concatenation
• Example SplitAndSubString.html fig. 12.6

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Date Object

• Access and format date and time
• See definitions at W3Schools
• Example DateTime.html fig. 12.9

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Document and Window Objects

• Document object allows access to all components
  of a document
• See definitions at W3Schools
• Window object allows control of window features
• See definitions at W3Schools
• Example Window.html fig. 12.13

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Cookies

• Accessed through Document cookie property
• Example cookie.html fig. 12.15

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Final Example

• final.html fig. 12.16