JavaScript Lecture 8

1
JavaScript Lecture 8

• Assignment (loops)
• What is an object?
• Array object
• Rules (text)
• Example using arrays

2

• Book
• Author
• Subject
• Cover color
• Edition
• No. of pages
• In braces are the properties of a general
  category of things called Book. Compare this with
  a class.

3

• Book Fluency with IT
• Author Lawrence Snyder
• Subject IT
• Cover color Pink
• Edition 2nd ed.
• No. of pages 766
• Now we are talking about a specific book
  Fluency with IT. Values are assigned to
  properties to describe this book.
• This is comparable with an object.

4
Object

• User created data-type
• Objects have properties and methods
• Methods are used to perform action
• example studyforquiz() could be a method for
  the object book
• This method can be called just like any other
  method or function
• example document.write()

5

• JavaScript is an Object Oriented Programming
  Language i.e. OOP
• An OOP language allows object definitions and
  user-created data types
• Built-in JavaScript objects
• example document, string, Array

6
Array

• The Array object is used to store a set of
  values in a single variable name.
• (www.w3schools.com)
• Note the A in Array
• Built-in JavaScript object
• Has properties and methods associated with it.

7

• artist_1, artist_2,.artist_5.
• Could you somehow store all these values in a
  single variable name artist?
• Yes!!
• artist5

8

• team10
• This array describes a team of 10 players.
• The players can be referenced as team0,
  team1, ..team9
• An Array is thus a collection of variables of the
  same data type and (usually) the same size.

9
Defining Arrays

• var team new Array()
• team0 Red Sox
• team1 Mets
• team2 Phillies
• Or var team new Array(3)
• team0 Red Sox
• team1 Mets
• team2 Phillies
• Or var team new Array(Red Sox, Mets,
  Phillies)

10

• (team0, team1, team5)
• i5
• Document.write(teami)

11
Accessing Arrays using the index

• var team new Array()
• team0 Red Sox
• document.write(team0)
• team0 Pirates
• document.write(team0)
• document.write(team10)
• Var a
• document.write(a)

12

• Output
• Red Sox
• Pirates
• undefined

13
Numeric and Boolean Arrays

• Similarly numbers or boolean values could be used
  inside arrays
• var submarks new Array(90, 70, 120)
• var boolarray new Array(true, true, false
• Csubmarks1 submarks2

14
Using for loops to access arrays

• lthtmlgt
• ltheadgtlttitlegt"Array1"lt/titlegtlt/headgt
• ltbodygt
• ltscript type"text/javascript"gt
• var team new Array()
• team0 "Red Sox"
• team1 "Mets"
• team2 "Phillies"
• for (i0ilt3i)
• document.write(teami)
• document.write("ltbrgt")

15

• var marks new Array(250)
• marks0 100
• Marks1120
• C marks0 marks1