Sams Teach Yourself JavaScript in 24 Hours
- 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
- 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
Which Script Runs First?
As you learned in Hour 1, you can actually have several scripts within a Web document: one or more sets of <script> tags, and any number of event handlers. With all of these scripts, you might wonder how the browser knows which to execute first. Fortunately, this is done in a logical fashion:
- Sets of <script> tags within the <head> section of an HTML document are handled first. Since these scripts cannot create output in the Web page, it's a good place to define functions for later use.
- Sets of <script> tags within the <body> section of the HTML document are executed after those in the <head> section, while the Web page loads and displays. If there is more than one script in the body, they are executed in order.
- Event handlers are executed when their events happen. For example, the onLoad event handler is executed when the body of a Web page loads. Since the <head> section is loaded before any events, you can define functions there and use them in event handlers.
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