This document discusses iterators, iterables, and generators in JavaScript. It explains that iterators must have a next() method to return the next value from a collection, while iterables must have a [Symbol.iterator] method that returns an iterator. Generators allow asynchronous code to run synchronously by pausing and resuming using the yield keyword. They produce iterables and allow two-way communication, making them useful for tasks like asynchronous functions.

1. Iterable, Iterator, Generator
By
Gaurav Khurana

2. Iterator Object
• Object is an Iterator object when it allows to access items from a
collection one at a time.
• Provide next() method to achieve above.
• next() method spits out object of this sort
{value : ”something” , done : true/false}.

3. Iterable interface
• Object must provide default iteration method which returns an
iterator object.
• [Symbol.iterator] is such method in javascript.
• Its automatically gets called by for of loop.

4. Symbol.iterator with other objects

5. Some objects doesn’t have iterable Interface

6. For of loop execute iterable interface
Log Result

7. No iterable for Objects?

8. But previous example restricts us to use keys
as number lets solve that

9. Quick Recap
• The Iterable interface require the implementation of a
[Symbol.iterator] method.
• The iterator interface require the implementation of next.
• Why next()?
• Because next method’s result has a done property set to true means the iterator has
been exhausted and the iteration value.
• Most Iterators implement Iterable interface i.e. most of them have
[Symbol.iterator] method.

10. Let’s simplify the confusing part

11. Simplifying further, the need of it

12. Array methods returns Iterable iterator

13. Generators
• Pause Run Pause.
• Blocking the asynchronous function calls.
• Implementing Iterables.

14. Conventional function running
Result

15. How generators are different?
• Can be pause as many times and resumed later.
• Allowing other code to run during these pause periods.
• ES6 generator functions are "cooperative" in their concurrency
behavior which basically indicates that a process (in our case, a
function) itself chooses when it will allow an interruption, so that it
can cooperate with other code.
• Use yield keyword to pause itself.

16. Syntax please ?

17. Generators produce iterables

18. Communicating with Generators

19. Where can we use them?

20. Two way communication with Generator

21. Array index using for of loop?

22. Generators can help attaining array index
using for of

23. Error Handling

24. Reverse Direction Error Handling

25. Reverse error handling continue

26. Delegating Generators with yield*

27. Delegating and accepting returned value

28. Generator can be used for async ajax

29. Using generator for async