7/29/2019 n341 de ObjectBasedJavascript

1/13

Copyright 2005 Department of Computer & Information Science

Object Based JavaScript

7/29/2019 n341 de ObjectBasedJavascript

2/13

Copyright 2005 Department of Computer & Information Science

Goals

By the end of this lecture you should

7/29/2019 n341 de ObjectBasedJavascript

3/13

Copyright 2005 Department of Computer & Information Science

REVIEW: What is an object?

An object is a unique programming entitythat has attributes to describe it andmethods to retrieve/set attribute values.

We can create a blueprint of an objectcalled a class.

We can create a usable instance of a classthrough instantiation.

7/29/2019 n341 de ObjectBasedJavascript

4/13

Copyright 2005 Department of Computer & Information Science

REVIEW: Encapsulation

Data and the ways to get at that dataare wrapped in a single package, a

class. The only way to access suchdata is through that package. Thisidea translates to information hiding.

7/29/2019 n341 de ObjectBasedJavascript

5/13

Copyright 2005 Department of Computer & Information Science

REVIEW: Inheritance

Inheritance allows programmers tocreate new classes from existing

ones.A child class inherits its properties

and attributes from its parents, which

programmers can change.

7/29/2019 n341 de ObjectBasedJavascript

6/13

Copyright 2005 Department of Computer & Information Science

REVIEW: Polymorphism

Polymorphism describes howprogrammers write methods to do

some general purpose function. Different objects might perform

polymorphic methods differently.

7/29/2019 n341 de ObjectBasedJavascript

7/13

Copyright 2005 Department of Computer & Information Science

Is JavaScript Object-Oriented?

Well, not really. Well call it Object-Based instead

JavaScript uses objects by way ofsupporting inheritance andencapsulation, but it doesn't really

provide support for polymorphism.

7/29/2019 n341 de ObjectBasedJavascript

8/13

Copyright 2005 Department of Computer & Information Science

Object-Based JavaScript

We can create new, custom, re-usableobjects in JavaScript that include theirown methods, properties and events.

Consider the following problem: I want torecord the color, brand, horsepower andprice of several cars.

7/29/2019 n341 de ObjectBasedJavascript

9/13

Copyright 2005 Department of Computer & Information Science

Solution Without Objects

One solution to our problem is to relyon parallel arrays.

However this can be confusing, as itcan be difficult to track with attributebelongs to which car

7/29/2019 n341 de ObjectBasedJavascript

10/13

Copyright 2005 Department of Computer & Information Science

Open the file calledobjectBasedProg_01.html

7/29/2019 n341 de ObjectBasedJavascript

11/13

Copyright 2005 Department of Computer & Information Science

What is an API?

API stands forApplicationProgramming Interface.

APIs allow programmers to extendthe current language to includedcustomized, re-usable components.

Most modern languages incorporateAPIs.

7/29/2019 n341 de ObjectBasedJavascript

12/13

Copyright 2005 Department of Computer & Information Science

Open the files calledobjectBasedProg_02.html &carLib.js

7/29/2019 n341 de ObjectBasedJavascript

13/13

Copyright 2005 Department of Computer & Information Science

Summary