This document discusses how to prevent "callback hell" in JavaScript code. It defines callback hell as hard to understand code from nested callbacks. It recommends naming functions clearly, defining new functions, and using Promise objects and generators to avoid callback nesting. Specifically, it suggests using the co library to wrap Promise objects in generator functions so code can use yield instead of nested callbacks. In conclusion, callback nesting is part of JavaScript but there are options like Promises or naming callbacks well to make code more readable.

1. How to Prevent
Callback Hell
Tianyu ZHAO

2. Self-Introduction
From China
Joined Drecom 1 year ago
Rails Developer

3. What is callback hell?

4. Why should we deal with it?
Hard to Understand

5. How to avoid this?

6. Name your functions

7. Define new functions

8. Use Promise object

9. Use Promise object
Create custom getJSON function

10. Use Promise object
Use custom getJSON function

11. Use Promise object
Don’t have to do that at all (Deferred Object in jQuery 1.8+)
http://api.jquery.com/category/deferred-object/

12. Use Promise + Generator
What’s Generator?

13. Use Promise + Generator
More about Promise

14. Use Promise + Generator
More about Promise

15. Use Promise + Generator
Cool Library: co (https://github.com/tj/co)
yield Promise

16. Use Promise + Generator
Cool Library: co (https://github.com/tj/co)
Promise
resolver
resolver
Generator
.next()
Promise
resolver

17. Conclusion
Callback hell is kind of the feature of JavaScript
Some people like it, some people don’t like it
Decide how to handle it by oneself (simply name functions
or use Promise + Generator)

18. Thank you!