Redux Thunk vs. Saga: Choosing the Right Middleware For Asynchronous Actions

Comparing Redux Thunk vs Saga helps developers choose the right middleware for handling asynchronous actions in React applications. This blog explains how each works, their strengths, limitations, and practical examples to guide your next project decision.

What if handling complex async logic in your app felt as predictable as updating a counter?

For most developers, managing state in large applications is anything but simple. Between synchronous updates, asynchronous actions, API calls, and other side effects, things can quickly get messy. Redux middleware steps in to bring order, extending how Redux works and keeping the application state consistent.

Among the most widely used middleware, two stand out: Redux Thunk and Redux Saga. Both aim to solve similar problems but take very different routes—one focuses on simplicity, while the other offers advanced control with generator functions.

In this blog, we’ll unpack Thunk vs Saga—exploring how they work, when to use them, and the trade-offs that can shape your next project decision.

Understanding Redux Middleware

Middleware in Redux acts as a bridge between the store’s dispatch method and the reducers. It intercepts an incoming action before it reaches the reducer, allowing for the execution of asynchronous code, logging, or calling external APIs.

In large projects, middleware allows software engineers to manage asynchronous data flow in a predictable and testable manner.

What is Redux Thunk?

Redux Thunk is a middleware that allows you to write asynchronous code within action creators. Instead of returning a plain action object, an action creator can return a function. This function receives dispatch as an argument, allowing developers to handle asynchronous actions in a step-by-step manner.

What's Redux Thunk?

“Middleware for writing functions in Redux, ideal for handling async tasks and complex logic.” → Check out the full post here

How Redux Thunk Works

• Action creators that return a function are intercepted by redux thunk.
• The function can run async functions, such as API calls.
• Once the response arrives, the function dispatches a new action object with the data.

For example:

Copy
1const fetchUsers = () => {
2  return async (dispatch) => {
3    dispatch({ type: "USERS_REQUEST" });
4    const response = await fetch("/api/users");
5    const data = await response.json();
6    dispatch({ type: "USERS_SUCCESS", payload: data });
7  };
8};
9

This example demonstrates how Redux Thunk facilitates writing asynchronous code within action creators while maintaining pure reducers.

What is Redux Saga?

Redux Saga is another middleware designed for handling side effects. Unlike Redux Thunk, which uses functions, Redux Saga relies on generator functions that can be paused and re-entered. This gives developers precise control over asynchronous actions and other side-effect management.

How Redux Saga Works

• Redux saga listens to specific triggers from action creators.
• A generator function handles asynchronous operations step by step.
• The method returns an iterator object that yields effects until the saga completes.

For example:

Copy
1import { call, put, takeEvery } from "redux-saga/effects";
2
3function* fetchUsersSaga() {
4  try {
5    const response = yield call(fetch, "/api/users");
6    const data = yield response.json();
7    yield put({ type: "USERS_SUCCESS", payload: data });
8  } catch (error) {
9    yield put({ type: "USERS_FAILURE", error });
10  }
11}
12
13function* rootSaga() {
14  yield takeEvery("USERS_REQUEST", fetchUsersSaga);
15}
16

Here, the generator function creates an iterator object that the saga middleware executes like a separate thread.

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Comparing Thunk and Redux Saga

Both Redux Thunk and Redux Saga extend the capabilities of Redux by handling asynchronous actions. Yet their approaches are quite different.

Ease of Writing and Learning

Redux Thunk is simpler to learn because it only involves writing functions inside action creators. For small to medium projects, thunk can handle most asynchronous needs, such as API calls. On the other hand, Redux Saga has a steeper learning curve due to its use of generator functions and advanced patterns.

Control Over Side Effects

Saga provides more power for handling complex side effects. A software engineer working with multiple API calls, event channels, or other components can rely on Saga generator function model to orchestrate asynchronous data flow. Unlike Redux Thunk, Saga can cancel tasks, restart flows, and run multiple effects concurrently.

Testing Capabilities

One major benefit of Redux Saga is its ability to test side effects easily. Since generator functions return iterator objects, tests can simulate step-by-step process execution without running real API calls. Redux Thunk can also be tested, but the process often requires mocking async functions.

Performance and Scalability

Both Redux Thunk and Redux Saga perform well for both regular synchronous actions and asynchronous actions. Yet, for projects that require the orchestration of multiple asynchronous operations, a saga provides a cleaner separation of concerns.

Redux Thunk may start to show limitations when handling complex workflows, while Saga scales better.

Practical Examples: Thunk vs Saga

Example with Redux Thunk

Copy
1const fetchData = () => {
2  return (dispatch) => {
3    dispatch({ type: "FETCH_REQUEST" });
4    return fetch("/api/data")
5      .then((res) => res.json())
6      .then((data) => {
7        dispatch({ type: "FETCH_SUCCESS", payload: data });
8      });
9  };
10};
11

This example demonstrates how Redux Thunk handles asynchronous actions within an action creator.

Example with Redux Saga

Copy
1function* fetchDataSaga() {
2  try {
3    const response = yield call(fetch, "/api/data");
4    const data = yield response.json();
5    yield put({ type: "FETCH_SUCCESS", payload: data });
6  } catch (error) {
7    yield put({ type: "FETCH_FAILURE", error });
8  }
9}
10

This saga example demonstrates how generator functions return effects that saga middleware executes step by step.

Which One Should You Use?

The answer depends on your project.

• If you are building a simple React app with limited asynchronous actions, Redux Thunk is often enough.
• For projects that require coordination of asynchronous operations, retries, or cancellation, Redux Saga offers more power.

Some developers also combine Redux Toolkit with Thunk for simpler workflows, while others opt for Saga for more complex enterprise-grade applications.

Final Thoughts: Choosing Between Redux Thunk and Saga

Both Redux Thunk and Redux Saga extend Redux to handle asynchronous code and side effects. Redux Thunk shines in smaller projects where simplicity is paramount, while Redux Saga excels in large applications that require the orchestration of complex, asynchronous data flows.

The choice between them depends on your project size, the number of API calls you expect, and the preference of your software engineering team. In short, when comparing Redux Thunk vs Saga, consider the complexity of your application state and long-term scalability needs.