JavaScript Object Programming - Introduction to Java Script - Lecture Slides, Slides of Javascript programming

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Object-Oriented Java Script

Object-Oriented

JavaScript

Objectives

• Study object-oriented programming
• Learn about the built-in JavaScript objects
• Work with the Array, Date, Math, and Number objects
• Define custom JavaScript objects

Reusable Software

• Object-oriented programming (OOP):
  • Refers to the creation of reusable software objects that can be easily incorporated into multiple programs
• Object:
  • Specifically refers to programming code and data that can be treated as an individual unit or component

Reusable Software (Cont.)

• Data:
  • Refers to information contained within variables or other types of storage structures
• Objects can range from simple controls such as a button, to entire programs such as a database application - In a retail sales program, you could refer to all the code that calculates the sales total as a single object. - You could reuse the object over and over again in the same program by typing the object name.

Encapsulation

• Objects are encapsulated:
  • All code and required data are contained within the object itself
• Encapsulation:
  • Places code inside what programmers like to call a “black box”
  • When an object is encapsulated, you cannot see “inside” it—all internal workings are hidden

Encapsulation (Cont.)

• The code (methods and statements) and data (variables and constants) contained in an encapsulated object are accessed through an interface
• Interface:
  • Represents elements required for a source program to communicate with an object - Interface elements required to access a Payroll object might be a method named calcNetPay()

Encapsulation (Cont.)

• Encapsulation prevents other programmers from:
  • Accidentally introducing a bug into a program
  • Stealing the code and claiming it as their own

Encapsulation (Cont.)

Classes (Cont.)

• A particular instance of an object inherits its methods and properties from a class:
  • It takes on the characteristics of the class on which it is based
  • For Example Consider an object called BankAccount that contains methods and properties that you might use to record transactions associated with a checking or savings account - The BankAccount object is created from a BankAccount class - To use the BankAccount class you create an instance of the class - A particular instance of an object inherits its methods and properties from a class - The BankAccout object inherits all its methods and properties from the BankAccout class

Classes (Cont.)

• Class names in traditional object-oriented programming usually begin with an uppercase letter. This convention is also followed in JavaScript

Instantiating an Object

• You can use some of the built-in JavaScript objects directly in your code - document.write(“The value of PI is “ + Math.PI);
• Other objects require you to instantiate a new object
  • var studentList = new Array()

Garbage Collection

• When you instantiate a new object, you are reserving memory
• Refers to cleaning up, or reclaiming, memory that is reserved by a program
• JavaScript knows when a program no longer needs a variable or object - Automatically cleans up the memory

Array Class Methods

The Length Property

• Returns the number of elements in an array
• You append the length property to the name of the array you want to sort using the following syntax: array_name .length;