JavaScript%20I

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JavaScript I
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• JavaScript is an object oriented programming
  language used to add interactivity to web pages.
• Different from Java, even though bears some
  syntactic resemblance.
• Enables control of the content of web pages,
  browsers and HTML forms.
• It is a case-sensitive language.
• Uses of JavaScript
• Client side validation of form data, prior to
  submission
• Performing arbitrary computations
• Controlling document appearance and content
• In combination with CSS, for creating DHTML
  (Dynamic HTML).

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• Enabling user interactivity by displaying
  messages or alert boxes in response to user
  input.
• Read and write client state with cookies
• Producing animation effects with images
• Interaction with Java applets
• Comments in JavaScript
• // for single line comments
• /./ for multiple line comments
• Literals
• A literal is a data value that appears directly
  in a program e.g. a string of text or a numeric
  value.

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• Identifiers
• An identifier is simply a name.
• Used to name variables and functions in
  JavaScript.
• Rules for identifiers are similar to those in
  Java and other programming languages
• The first character must be a letter, an
  underscore _, or
• Subsequent characters can be a letter or digit.
• Reserved words
• These are words that can not be used as
  identifiers, as they are part of the language
  syntax. Include words such as break, case, catch,
  continue, default, delete, do, else, false,
  finally, for, function, if, in, new, null,
  return, switch, this, throw, true, try, var, void
  and while.

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• Data Types
• The types of values that can be represented and
  manipulated by a programming language
• JavaScript supports
• Numbers
• Strings (strings of text)
• Boolean values
• Object An object is a composite data type that
  represents a collection of values such as numbers
  and strings, or other objects.
• Numbers
• Most basic data type.
• Represented in JavaScript as floating-point
  values
• Can represent numbers as large as
  1.797693134862315710308 and as small as 510-324

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• Strings
• A sequence of Unicode letters, digits and
  punctuation marks enclosed in matching pairs of
  single or double quotation marks.
• Double-quote character should be enclosed in
  single quotation marks
• Single-quote enclosed in double quotation marks
• Escape sequences in string literals
• \n creates a new line
• \ represents the single quote or apostrophe e.g
  You\re not would translate to Youre not
• \\ represents backslash, and \r represents
  carriage return.

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• Working with Strings
• Concatenation JavaScript has a built-in feature
  that allows joining one string to another with
  the operator e.g We have moved on to
  JavaScript results in We have moved on to
  JavaScript
• Length Determines the numbers of characters
  contained in a string. E.g. to determine the
  number of characters in a variable called s, the
  syntax is s.length
• To get the last character in a string last_char
  s.charAt(s.length 1)
• To find the position of the first letter a in a
  string s, position_of_a s.indexOf(a)

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• Boolean Values
• Has only 2 possible values (True or False)
• Generally the result of comparisons made within a
  script.
• Typically used in control structures e.g if/else
  statements perform one action if a boolean value
  is true and another action if the value is false.
• Functions
• Piece of executable code that is defined by a
  JavaScript program, or predefined by the
  JavaScript implementation.
• Defined only once, but can be executed or invoked
  any number of times.
• May be passed arguments or parameters that
  specify value(s) upon which it is to perform its
  computation.

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• Functions (contd.)
• May return value that represents the results of
  computation.
• JavaScript implementations provide many
  predefined functions, such as Math.sin() function
  that computes the sine of an angle.
• Example
• function square(x) // the function is named
  square and expects //
  one argument, x. The body is enclosed in
• return xx // curly brackets. This
  function squares its
• // argument and
  returns the value.
• Invoking Functions
• b square(x)
• y Math.sin(x)

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• Objects
• Collection of named values
• The named values are usually referred to as
  properties of the object.
• The properties are usually represented as the
  name of the object followed by a period (.),
  followed by the name of the property e.g. if an
  object named image has properties named width and
  height, theyll be represented as image.width and
  image.height, respectively.
• Creating Objects
• Objects are created by invoking special
  constructor functions.
• var o new Object()
• Once created, you can use and set its properties
  e.g.
• var point new Object() point.x 2.3 point.y
  4.5

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• Object Literals
• Also called object initializer.
• The point object can be created and initialized
  with the following code
• var point x2, y4
• Object literals can also be nested. E.g.
• var rectangle upperLeft x2, y4 ,
• lowerRight
  x6, y10
• The property values used in object literals do
  not have to be constants, i.e. they could be
  expressions e.g.
• var rectangle upperLeft xpoint.x,
  ypoint.y ,
• lowerRight x(point.x
  ln), y(point.y ln2)

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• Arrays
• Collection of data values, similar to an object.
• While each data value in an object has a name,
  each data value in an array has an index.
• The index is a positive integer.
• Arrays may contain any type of JavaScript data,
  including references to other arrays or objects
• Example If an array is named a, and n is a
  positive integer, an is an element of the
  array.
• Array indexes begin with zero, therefore a2 is
  the third element of the array a.
• References Dietel, Dietel Nieto Chapter 8
• JavaScript The Definitive guide 4th Ed. David
  Flanagan. Chapters 1, 2 3