But you should read this anyway… As the async/await syntax continues to grow in popularity, so does curiosity about their inner workings. It’s easy enough to piece together through a that the underpinnings of async/await is a combination of Promises(ok, sure I know Promises) and Generators(huh?). google search The purpose of this article is as follows: explore basic Generator functionality talk about how Generators + Promises = async/await make the argument that you don’t need to worry about learning Generators this article assumes basic knowledge of Promises some Iterators and Generators — but mostly Generators Starting with ES6, there have been several new functions added to the language that aim to make dealing with asynchronous data streams and collections of objects easier. fall in this category. Iterators and Generators are powerful in that they provide a means to access items in a collection one at a time, while keeping track of the current index. Iterators https://gist.github.com/btg5679/91048cc658db67594b6fe2bca4c70ef1 Above we pass in a simple array with 2 values and we iterate over the values by calling it.next(). Note the full commented responses. Now for Generators are functions that serve as a factory for . Let’s look at a basic example, then we will discuss the 2 basic parts of a Generator, the and the . Generators. Iterators Generator Function Generator Iterator https://gist.github.com/btg5679/d830f0067e5ae1610459131d38ce636e Note the syntax, the indicates that the function is a generator and the keyword which pauses function execution( 😮) and returns(yields) a value. asterisk yield Earlier I mentioned the 2 parts of a Generator: — defined with an asterisk the function name or keyword Generator Function near — created when you invoke the Generator Function Generator Iterator So here we see the Generator Factory at work, Generating Iterators. At this point, things begin to get more interesting. Communication with Generators can happen in both directions, Generators can values to Iterators, but Iterators can also send values to Generators in the method. yield iterator.next('someValue') https://gist.github.com/btg5679/ffe53b3522abeb49ac11ea9844890899 Generators + Promises Now we can talk for a moment about how Generators and Promises form the foundation for the async/await expression. Imagine for a moment that instead of yielding values the Generator yielded Promise functions. You could then wrap the generator in a function that could wait for the Promise to resolve and return the Promise value to the Generator in the .next() method as we just demonstrated. There is a popular library called that does just that. Really simply, something like this: coroutines Do I need it? My opinion of Generators is that you need them in order for async/await to work, but you don’t need to learn to incorporate them directly into your code. Generators introduce to JS the ability to pause function execution and return to it when(if) we see fit. Up until now we expected functions to run to their completion upon execution. This is a revelation, but one that async/await neatly wraps up for us. Some of the counter arguments are that bundled code devolves async/await into generators so, being familiar with Generators may help you in the debug process. I view that differently though that trying to find ways to incorporate Generators into your code directly. That’s all for this round. We covered Iterator and Generator basics, how Generators + Promises got us to async/await and why you should not try and force Generators into your JS repertoire. What are your thoughts on Generators? Is there a use case that I am not thinking of? Let me know your thoughts and questions and give me a follow on . Keep after it. twitter Further Reading that I found helpful: https://blog.benestudio.co/async-await-vs-coroutines-vs-promises-eaedee4e0829 _IntroductionHave you ever needed to loop through a list, but the operation took a significant amount of time to…_code.tutsplus.com Using Iterators and Generators in JavaScript to Optimize Code _In 7 Surprising Things I Learned Writing a Fibonacci Generator in JavaScript, I covered one obvious use-case for ES6…_medium.com The Hidden Power of ES6 Generators: Observable Async Flow Control https://hackernoon.com/async-await-generators-promises-51f1a6ceede2
