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
    • Using for Loops
    • Using while Loops
    • Using do...while Loops
    • Working with Loops
    • Using for...in loops
    • Workshop: Working with Arrays and Loops
    • Summary
    • Q&A
    • Quiz
    • Exercises
  • 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
  • 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

Using for...in loops

A third type of loop is available in JavaScript. The for...in loop is not as flexible as an ordinary for or while loop. Instead, it is specifically designed to perform an operation on each property of an object.

For example, the navigator object contains properties that describe the user's browser, as you'll learn in Hour 14, "Creating Cross-Browser Scripts." You can use for...in to display this object's properties:

for (i in navigator) {
document.write("property: " + i);
document.write(" value: " + navigator[i] + "<br>");
}

Like an ordinary for loop, this type of loop uses an index variable (i in the example). For each iteration of the loop, the variable is set to the next property of the object. This makes it easy when you need to check or modify each of an object's properties.

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