This Collection of Common Redux-Saga Patterns Will Make Your Life Easier

Managing complex asynchronous operations is one of the biggest challenges in building robust React/Redux applications. While Redux itself is a simple state management library, integrating it with async actions like API requests, background processes, and data synchronization can quickly lead to confusion.

Enter Redux-Saga – a powerful middleware library that brings clarity and testability to your Redux application‘s side effects. By leveraging ES6 generators, Redux-Saga allows you to write asynchronous code that looks synchronous, avoiding callback hell and dramatically simplifying your application‘s control flow.

Over the past few years of building large-scale Redux applications with Redux-Saga at CompanyX, my team and I have identified several common patterns that have allowed us to ship high-quality features faster. By standardizing on these patterns across teams, we‘ve been able to increase code reuse, reduce bugs, and onboard new developers more quickly.

In this post, I‘ll share five of the most useful Redux-Saga patterns we‘ve adopted. For each one, I‘ll describe the pattern, provide a real-world use case, and show a concrete code example. Whether you‘re a seasoned Redux-Saga user or just getting started, I hope you‘ll find some valuable takeaways to apply in your own projects.

The Benefits of Redux-Saga

Before diving into specific patterns, let‘s briefly review what Redux-Saga is and why you might want to use it. In short, Redux-Saga is a library that aims to make application side effects (i.e. asynchronous things like data fetching and impure things like accessing the browser cache) easier to manage, more efficient to execute, simple to test, and better at handling failures.

The mental model is that a saga is like a separate thread in your application that‘s solely responsible for side effects. Redux actions are side-effect-free objects that describe something that happened in the application. Sagas listen for these actions and coordinate the appropriate side effects in response.

Some key benefits of using Redux-Saga:

1. Maintainable Code: By moving side effects into sagas, your Redux reducers become simple, pure functions that are easy to test and reason about. This leads to more maintainable code overall.

2. Testable Asynchronous Flows: Sagas are easy to test because you can simply iterate over the generator function and test the effects emitted. You can also test the actual executed side effects separately.

3. Efficient Execution: Sagas are implemented using generator functions that allow them to be paused and resumed at any point. This allows for more efficient execution, especially when dealing with multiple, complex asynchronous operations.

4. Better Error Handling: Sagas can catch errors in effects and allow the app to recover gracefully without crashing. They provide a centralized, standardized way of handling errors across the application.

5. Modular Design: Sagas promote a modular design where each saga is responsible for a specific feature or flow in the application. This makes the codebase more maintainable as it grows over time.

With those benefits in mind, let‘s jump into some specific patterns your team can leverage to take full advantage of Redux-Saga.

The Take and Fork Pattern

One of the most common scenarios in a web application is needing to trigger a background process in response to a specific user action. For example, when a user clicks a "Load More" button, you may need to fetch the next page of data from the server and add it to the UI.

The "Take and Fork" pattern is perfect for these situations. The basic idea is:

1. The saga listens for (takes) a specific action.
2. When that action is dispatched, the saga triggers (forks) a new task to handle the work.

Here‘s what it looks like in code:

import { take, fork } from ‘redux-saga/effects‘;
import { fetchPage } from ‘./api‘;

function* watchLoadMore() {
  while(true) {
    const { payload } = yield take(‘LOAD_MORE‘);
    yield fork(loadMore, payload);
  }
}

function* loadMore(page) {
  const data = yield call(fetchPage, page);
  yield put({ type: ‘PAGE_LOADED‘, payload: data });
}

In this example, watchLoadMore is a saga that listens for LOAD_MORE actions using the take effect. Each time that action is dispatched (e.g. when the user clicks the button), it forks a new loadMore task to fetch the data and dispatch a PAGE_LOADED action with the result.

By using fork, the watchLoadMore saga is able to continue listening for LOAD_MORE actions even while the loadMore task is still pending. This allows the user to queue up multiple requests if they click rapidly.

The Watch and Fork Pattern

The "Take and Fork" pattern works well for one-off async flows, but what if you need to handle a particular action continuously? For example, you may have a web socket connection that can dispatch many INCOMING_MESSAGE actions over time and each one needs to be handled.

In this case, the idiomatic approach is to create a saga that continuously watches for a particular action using a while(true) loop and the take effect. Each time the action is dispatched, you fork a new task to handle that particular instance.

Here‘s an example:

import { take, fork, call, put } from ‘redux-saga/effects‘;
import { processMessage } from ‘./processMessage‘;

function* watchIncomingMessages() {
  while (true) {
    const action = yield take(‘INCOMING_MESSAGE‘);
    yield fork(handleMessage, action.payload);
  }
}

function* handleMessage(message) {
  const result = yield call(processMessage, message);
  yield put({ type: ‘MESSAGE_PROCESSED‘, payload: result });
}

This watchIncomingMessages saga will continuously watch for INCOMING_MESSAGE actions using while(true) and the take effect. Each time an action is dispatched, it forks a new handleMessage task to process that specific message and dispatch a MESSAGE_PROCESSED action with the result.

This pattern ensures that every single INCOMING_MESSAGE action is handled, even if many are dispatched in rapid succession. It‘s a powerful way to manage complex real-time flows in your application.

The Put and Take Pattern

In more complex scenarios, you may have multiple sagas that need to coordinate with each other to complete an overall flow. The "Put and Take" pattern is a way to communicate between sagas using actions.

The basic idea is:

1. Saga A dispatches (puts) an action.
2. Saga B listens for (takes) that action and responds accordingly.

Here‘s a simple example:

import { take, put } from ‘redux-saga/effects‘;

function* sagaA() {
  yield put({ type: ‘SAGA_A_DONE‘ });
}

function* sagaB() {
  yield take(‘SAGA_A_DONE‘);
  console.log(‘Saga A is done!‘);
}

In this case, sagaA simply dispatches a SAGA_A_DONE action using the put effect. sagaB listens for that specific action using take. When the action is dispatched, sagaB logs a message.

A more real-world example might be a user registration flow. When the user submits the registration form, sagaA could dispatch a REGISTRATION_SUBMITTED action. sagaB could listen for that action, call an API to create the user account, and then dispatch a REGISTRATION_SUCCEEDED or REGISTRATION_FAILED action depending on the result. sagaA could then listen for those actions to display a success message or error to the user.

By using actions to communicate, sagas can remain decoupled from each other while still coordinating to accomplish an overall goal. This leads to a more modular and maintainable saga architecture.

The For/Of Collection Pattern

Sometimes you need to perform an operation on each element of an array within a saga. For example, you may need to make an API request for each item in a user‘s shopping cart to get the latest price and availability.

While you could use the built-in forEach or map methods, sagas operate on generator functions which don‘t allow you to directly yield inside a callback. Instead, you can use a for...of loop to iterate over the array and yield effects for each item.

Here‘s an example:

import { call, put } from ‘redux-saga/effects‘;
import { fetchProductDetails } from ‘./api‘;

function* fetchCartDetails(cart) {
  for (const item of cart) {
    const details = yield call(fetchProductDetails, item.productId);
    yield put({ type: ‘PRODUCT_DETAILS_RECEIVED‘, payload: details });
  }
}

In this saga, we receive the user‘s cart as an argument. We then use a for...of loop to iterate over each item in the cart. For each item, we call the fetchProductDetails API with the item‘s productId, and then put a PRODUCT_DETAILS_RECEIVED action with the result.

By using a for...of loop, we can easily perform async operations on each element of the array while keeping our saga code linear and readable.

Error Handling

No discussion of asynchronous patterns would be complete without touching on error handling. After all, any async operation can potentially fail, and we need a way to gracefully handle those failures.

With Redux-Saga, the recommended approach is to use the try/catch statement to catch errors from yield expressions. You can then dispatch an error action to let the Redux reducers handle the error state.

Here‘s an example:

import Api from ‘./path/to/api‘
import { call, put } from ‘redux-saga/effects‘

function* fetchProducts() {
  try {
    const products = yield call(Api.fetch, ‘/products‘)
    yield put({ type: ‘PRODUCTS_RECEIVED‘, products })
  } catch (error) {
    yield put({ type: ‘PRODUCTS_REQUEST_FAILED‘, error })
  }
}

In this example, we call an API to fetch products. If the API request succeeds, we put a PRODUCTS_RECEIVED action with the fetched products. If an error is thrown (network error, timeout, etc.), we catch it and put a PRODUCTS_REQUEST_FAILED action instead.

By dispatching different actions for success and failure, we allow our reducers to update the state accordingly, potentially displaying an error message to the user.

It‘s a good practice to wrap any yield statements that may throw an error (particularly call and put) inside a try/catch block. This ensures that any potential errors are caught and handled within the saga itself.

Combining Patterns

While each of these patterns is useful on its own, the real power of Redux-Saga comes from combining them to handle complex async flows.

For example, you might have a saga that watches for a user action (using "Watch and Fork"), makes an API request (using "For/Of Collection" to iterate over an array of needed data), coordinates with other sagas (using "Put and Take" to communicate via actions), and handles errors every step of the way.

By leveraging the power and expressiveness of generator functions, Redux-Saga allows you to write these complex flows in a way that is easy to reason about and easy to test.

The Power of Shared Conventions

One of the biggest benefits we‘ve seen from adopting Redux-Saga patterns across our teams is the power of shared conventions.

When every team follows the same patterns for handling common async scenarios, it becomes much easier for developers to jump into unfamiliar parts of the codebase and understand what‘s going on. It also promotes code reuse, as sagas that follow established patterns can often be shared across features or even across projects.

By documenting and evangelizing these patterns within your organization, you can dramatically increase the coherence and maintainability of your Redux codebase as it grows over time.

Evolving Your Saga Architecture

As with any architecture, your Redux-Saga patterns should evolve over time as your application grows and changes.

Maybe you start out with a simple "Take and Fork" saga for a small feature, but as that feature grows in complexity, you refactor it into multiple sagas coordinated with "Put and Take." Maybe you find a particular error handling pattern works well for your team and standardize on it across all your sagas.

The key is to continuously reevaluate and refactor your sagas as you would any other part of your codebase. By keeping your sagas clean, concise, and adhering to well-established patterns, you can ensure that your async logic remains maintainable over the long run.

Conclusion

Redux-Saga is a powerful tool for managing asynchronous operations in your Redux applications. By leveraging generator functions and effects, it allows you to write complex async flows in a way that is easy to reason about and easy to test.

In this post, we‘ve covered five common Redux-Saga patterns that can help you handle a variety of async scenarios:

1. "Take and Fork" for triggering background processes on specific actions.
2. "Watch and Fork" for continuously handling actions over time.
3. "Put and Take" for coordinating multiple sagas.
4. "For/Of Collection" for iterating over arrays.
5. Try/Catch blocks for error handling.

We‘ve also discussed the power of standardizing on these patterns across teams, and the importance of continuously evolving your saga architecture as your application grows.

By adding these patterns to your toolkit and sharing them with your team, you‘ll be well on your way to building robust, maintainable Redux applications that can handle even the most complex async flows.