Iterable, Iterator, Generator

By Gaurav Khurana

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}.

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.

Symbol.iterator with other objects

Some objects doesn’t have iterable Interface

For of loop execute iterable interface

Log Result

No iterable for Objects?

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

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.

Let’s simplify the confusing part

Simplifying further, the need of it

Array methods returns Iterable iterator

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

Conventional function running

Result

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.

Syntax please ?

Generators produce iterables

Communicating with Generators

Where can we use them?

Two way communication with Generator

Array index using for of loop?

Generators can help attaining array index using for of

Error Handling

Reverse Direction Error Handling

Reverse error handling continue

Delegating Generators with yield*

Delegating and accepting returned value

Generator can be used for async ajax

Using generator for async