Sams Teach Yourself JavaScript in 24 Hours

By Michael Moncur

• Table of Contents
  • Copyright
  • About the Author
  • Acknowledgments
  • We Want to Hear from You!
  • Reader Services
  • Introduction
  • Part I: Getting Started
  • Hour 1. Understanding JavaScript
  • Hour 2. Creating a Simple Script
  • Hour 3. How JavaScript Programs Work
  • Part II: Learning JavaScript Basics
  • Hour 4. Using Functions and Variables
  • Hour 5. Using Strings and Arrays
  • Hour 6. Testing and Comparing Values
  • Hour 7. Repeating Yourself: Using Loops
  • Hour 8. Using Math and Date Functions
  • Part III: The Document Object Model (DOM)
  • Hour 9. Working with the Document Object Model
  • Hour 10. Responding to Events
  • Hour 11. Using Windows and Frames
  • Hour 12. Getting Data with Forms
  • Hour 13. Using Graphics and Animation
  • Part IV: Moving on to Advanced JavaScript Features
  • Hour 14. Creating Cross-Browser Scripts
  • Hour 15. Creating Custom Objects
    • Using Objects to Simplify Scripting
    • Creating an Object Instance
    • Customizing Built-In Objects
    • Workshop: Storing Data in Objects
    • Summary
    • Q&A
    • Quiz
    • Exercises
  • Hour 16. Working with Sounds and Plug-Ins
  • Hour 17. Debugging JavaScript Applications
  • Part V: Working with Dynamic HTML (DHTML)
  • Hour 18. Working with Style Sheets
  • Hour 19. Using Dynamic HTML (DHTML)
  • Hour 20. Using Advanced DOM Features
  • Part VI: Putting It All Together
  • Hour 21. Improving a Web Page with JavaScript
  • Hour 22. Creating a JavaScript Game
  • Hour 23. Creating DHTML Applications
  • Hour 24. JavaScript Tips and Tricks
  • Part VII: Appendices
  • Appendix A. Other JavaScript Resources
  • Appendix B. Tools for JavaScript Developers
  • Appendix C. Glossary
  • Appendix D. JavaScript Quick Reference
  • Appendix E. DOM Quick Reference

Creating an Object Instance

Now let's use the object definition and method you created above. To use an object definition, you create a new object. This is done with the new keyword. This is the same keyword you've already used to create Date and Array objects.

The following statement creates a new Card object called tom:

tom = new Card("Tom Jones", "123 Elm Street", "555-1234", "555-9876");

As you can see, creating an object is easy. All you do is call the Card() function (the object definition) and give it the required attributes, in the same order as the definition.

Once this statement executes, a new object is created to hold Tom's information. This is called an instance of the Card object. Just as there can be several string variables in a program, there can be several instances of an object you define.

Rather than specify all the information for a card with the new keyword, you can assign them after the fact. For example, the following script creates an empty Card object called holmes, and then assigns its properties:

holmes = new Card();
holmes.name = "Sherlock Holmes";
holmes.address = "221B Baker Street";
holmes.workphone = "555-2345";
holmes.homephone = "555-3456";

Once you've created an instance of the Card object using either of these methods, you can use the PrintCard() method to display its information. For example, this statement displays the properties of the tom card:

tom.PrintCard();

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