How do you handle asynchronous operations with Hooks?

React Hooks - Interview Questions and Answers

Handling Asynchronous Operations with Hooks in React

React Hooks don't have built-in support for asynchronous operations, but you can handle them using async functions, Promises, or libraries like axios and fetch. Here’s how you can manage async operations effectively.

1. Using `useEffect` for Side Effects (Fetching Data)

Since useEffect runs after render, it’s a great place to fetch data from an API.

Example: Fetching Data with `fetch`

import { useState, useEffect } from "react";

function FetchData() {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    const fetchData = async () => {
      try {
        const response = await fetch("https://jsonplaceholder.typicode.com/posts/1");
        if (!response.ok) throw new Error("Failed to fetch");
        const result = await response.json();
        setData(result);
      } catch (err) {
        setError(err.message);
      } finally {
        setLoading(false);
      }
    };

    fetchData();
  }, []); // Empty dependency array → runs once

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error: {error}</p>;
  return <p>Title: {data?.title}</p>;
}

* Key Takeaways :

Fetch inside useEffect to run the request when the component mounts.
Use async/await inside a function (not directly in useEffect).
Handle loading and error states properly.

2. Handling Asynchronous State Updates

State updates using useState are synchronous in React, but you can use useEffect to react to state changes asynchronously.

import { useState, useEffect } from "react";

function AsyncCounter() {
  const [count, setCount] = useState(0);
  const [doubleCount, setDoubleCount] = useState(0);

  useEffect(() => {
    const timer = setTimeout(() => {
      setDoubleCount(count * 2);
    }, 500);

    return () => clearTimeout(timer); // Cleanup
  }, [count]); // Runs when count changes

  return (
    <div>
      <button onClick={() => setCount(count + 1)}>Increment</button>
      <p>Count: {count}</p>
      <p>Double (delayed): {doubleCount}</p>
    </div>
  );
}

* Why use `useEffect`?

Prevents race conditions by cleaning up previous timers before setting a new one.
Ensures derived state updates asynchronously.

3. Using `useCallback` for Asynchronous Functions

If you're passing an async function as a prop to child components, wrap it in useCallback to prevent unnecessary re-renders.

import { useState, useCallback } from "react";

function FetchButton({ fetchData }) {
  return <button onClick={fetchData}>Fetch Data</button>;
}

function ParentComponent() {
  const [data, setData] = useState(null);

  const fetchData = useCallback(async () => {
    const response = await fetch("https://jsonplaceholder.typicode.com/posts/2");
    const result = await response.json();
    setData(result);
  }, []);

  return (
    <div>
      <FetchButton fetchData={fetchData} />
      <p>Data: {data?.title}</p>
    </div>
  );
}

* Why use `useCallback`?

Prevents unnecessary re-renders of child components that depend on fetchData.

4. Using `useReducer` for Complex Async State Logic

For managing complex async state (e.g., loading, success, failure states), use useReducer.

import { useReducer, useEffect } from "react";

const initialState = {
  loading: true,
  data: null,
  error: null,
};

function reducer(state, action) {
  switch (action.type) {
    case "SUCCESS":
      return { loading: false, data: action.payload, error: null };
    case "ERROR":
      return { loading: false, data: null, error: action.payload };
    default:
      return state;
  }
}

function FetchWithReducer() {
  const [state, dispatch] = useReducer(reducer, initialState);

  useEffect(() => {
    async function fetchData() {
      try {
        const response = await fetch("https://jsonplaceholder.typicode.com/posts/3");
        const result = await response.json();
        dispatch({ type: "SUCCESS", payload: result });
      } catch (err) {
        dispatch({ type: "ERROR", payload: err.message });
      }
    }
    fetchData();
  }, []);

  if (state.loading) return <p>Loading...</p>;
  if (state.error) return <p>Error: {state.error}</p>;
  return <p>Title: {state.data?.title}</p>;
}

* Why `useReducer`?

Better for handling complex async state transitions (loading, success, failure).
Makes state updates more predictable.

5. Using `useContext` for Asynchronous Global State

For fetching data once and sharing it globally, use useContext with a provider.

import { createContext, useContext, useState, useEffect } from "react";

const DataContext = createContext();

function DataProvider({ children }) {
  const [data, setData] = useState(null);

  useEffect(() => {
    async function fetchData() {
      const response = await fetch("https://jsonplaceholder.typicode.com/posts/4");
      const result = await response.json();
      setData(result);
    }
    fetchData();
  }, []);

  return <DataContext.Provider value={data}>{children}</DataContext.Provider>;
}

function DisplayData() {
  const data = useContext(DataContext);
  return <p>Title: {data?.title || "Loading..."}</p>;
}

function App() {
  return (
    <DataProvider>
      <DisplayData />
    </DataProvider>
  );
}

* Why `useContext`?

Avoids prop drilling when sharing async data across multiple components.

Best Practices for Handling Async in Hooks :

Best Practice	Do This
Use `useEffect` for API calls	Fetch data inside `useEffect`
Use `async` inside functions, not `useEffect` directly	Define async functions inside `useEffect`
Handle errors properly	Use `try/catch` and `setError` states
Cleanup side effects	Return a cleanup function inside `useEffect`
Use `useCallback` for async functions in props	Prevent unnecessary re-renders
Use `useReducer` for complex state updates	Manage loading, success, and error states

Handling Asynchronous Operations with Hooks in React

1. Using useEffect for Side Effects (Fetching Data)

Example: Fetching Data with fetch

* Key Takeaways :

2. Handling Asynchronous State Updates

* Why use useEffect?

3. Using useCallback for Asynchronous Functions

* Why use useCallback?

4. Using useReducer for Complex Async State Logic

* Why useReducer?

5. Using useContext for Asynchronous Global State

* Why useContext?