RFC: Introducing Sagas

[codehag]

We are going in a really excellent direction with our refactorings. One topic that came up during our work week was sagas. I did a little bit of drawing regarding how this would look from an architectural perspective:

A comparison of the two approaches:

Thunks:

Thunks are a promise based way of wrapping our dispatch action to handle asynchronous data. This is well suited when we have a simple asynchronous query. Simple here being defined as one responder, and at most one data change.

Pros:

• easy to get started, you wrap the action in a dispatch with promise middleware.
• Promises are easy to comprehend as they have been around for a while

Cons:

• thunks are called. They do not have control over when they are called or how. This can result in bubbling
• there is a single potential error handler, the catch block, which is called sequentially. no fine grained control on errors / roll back /roll forwards
• they are not composeable
• make actions and reducers difficult to test

Sagas:

Sagas rely on generators and sit between dispatched actions and the reducers they influence. They respond to actions and take care of multi-step data processing / server communicaton. This is best suited for distributed / long life transactions.

Pros:

• fine grained error handling / roll backs / roll forwards
• sagas call, and are not called. They have more control over how they are executed, this reduces bubbling.
• they return simple objects, sagas, reducers, and actions can be tested independantly

cons:

• rely on the generator pattern, which not many are familiar with
• require a large refactoring

Reading Material:

• Problems with Thunks and Sagas
• Redux side effects reading list
• Pros and cons of Redux Saga generators
• similar discussion

I still have a bit of thinking to do about this but am interested what others have on their minds!

[kwonoj]

Just throwing out question, feel freely ignore / discard 🙏 - has epics been considered as a candidate as well? (https://github.com/redux-observable/redux-observable/blob/master/docs/basics/Epics.md#epics)

[markerikson]

Hey, I recognize those first two links! :) Nice diagrams too, btw.

Not sure I have specific feedback to offer, beyond agreeing that sagas (and the equivalents from redux-observable / redux-logic ) are definitely great tools for setting up complex async workflows and decoupling parts of an app architecture.

You might also want to glance through some of the articles in the "Redux Architecture" section of my list, especially the "Variations" section - there's a few articles there that discuss interesting uses of sagas.

If there's any potential questions I can help answer, please let me know!

[jasonLaster]

Closing this issue as we're currently working on refactoring our redux thunk actions and will continue evaluating sagas as we go.

Thanks for all the input!