ArticleZip > React Hooks Why Do Several Usestate Setters In An Async Function Cause Several Rerenders

React Hooks Why Do Several Usestate Setters In An Async Function Cause Several Rerenders

When working with React, understanding how state and hooks work can make a big difference in how your components behave. One common issue that developers face is why using multiple `useState` setters in an async function can trigger multiple re-renders. Let's dive into this topic to understand what's happening behind the scenes and how you can optimize your code to avoid unnecessary re-renders.

React Hooks provide a way to add stateful logic to functional components. When you call `useState` within a component, React sets up the state and the respective setter function for that state. Each time a setter function is called, React re-renders the component to reflect the updated state.

In the case of using multiple `useState` setters within an async function, the issue arises due to how JavaScript handles asynchronous operations. When an async function is called, it starts executing asynchronously, and the subsequent code continues to run while the async operation is in progress. This means that if you call multiple `useState` setters within the async function, each setter triggers a state change, which in turn triggers a re-render.

To illustrate this, consider the following example:

Jsx

import React, { useState } from 'react';

const MyComponent = () => {
  const [count1, setCount1] = useState(0);
  const [count2, setCount2] = useState(0);

  const updateCounts = async () => {
    await someAsyncOperation(); // Simulating an async operation
    setCount1(count1 + 1);
    setCount2(count2 + 1);
  };

  return (
    <div>
      <button>Update Counts</button>
      <p>Count 1: {count1}</p>
      <p>Count 2: {count2}</p>
    </div>
  );
};

In this example, calling `updateCounts` triggers an async operation followed by updating `count1` and `count2` using their respective setters. Since `useState` triggers a re-render on state change, updating both counts within the async function leads to two re-renders, which may not be the desired behavior.

To address this issue and optimize the component to avoid unnecessary re-renders, you can batch state updates using `useReducer` or `Promise.all` to await multiple async operations. By batching state updates, you can ensure that the component only re-renders once after all state changes have been applied.

Here's an updated version of the previous example using `Promise.all` to batch state updates:

Jsx

import React, { useState } from 'react';

const MyComponent = () =&gt; {
  const [count1, setCount1] = useState(0);
  const [count2, setCount2] = useState(0);

  const updateCounts = async () =&gt; {
    await Promise.all([someAsyncOperation(), someAsyncOperation()]);
    setCount1(count1 + 1);
    setCount2(count2 + 1);
  };

  return (
    <div>
      <button>Update Counts</button>
      <p>Count 1: {count1}</p>
      <p>Count 2: {count2}</p>
    </div>
  );
};

By batching state updates within the async function, you can ensure that only a single re-render occurs after both state changes have been applied, optimizing the performance of your components.

In conclusion, when using multiple `useState` setters within an async function in React, it's crucial to be mindful of how state changes and re-renders are handled. By batching state updates using techniques like `Promise.all`, you can optimize your components and prevent unnecessary re-renders, enhancing the overall performance and user experience of your React applications.

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