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 while Loops

Another keyword for loops in JavaScript is while. Unlike for loops, while loops don't necessarily use a variable to count. Instead, they execute as long as a condition is true. In fact, if the condition starts out as false, the statements won't execute at all.

The while statement includes the condition in parentheses, and it is followed by a block of statements within braces, just like a for loop. Here is a simple while loop:

while (total < 10) {
n++;
total += values[n];
}

This loop uses a counter, n, to iterate through the values array. Rather than stopping at a certain count, however, it stops when the total of the values reaches 10.

You might have noticed that you could have done the same thing with a for loop:

for (n=0;total < 10; n++) {
total += values[n];
}

As a matter of fact, the for loop is nothing more than a special kind of while loop that handles an initialization and an increment for you. You can generally use while for any loop. However, it's best to choose whichever type of loop makes the most sense for the job, or that takes the least amount of typing.

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