Bad setState() call and possible solution while rendering!

Warning: Cannot update a component (Bookings) while rendering a different component (BookingConfirmationModal). To locate the bad setState() call inside BookingConfirmationModal, follow the stack trace as described!

In React applications, you'll often encounter this dreaded error. This error arises when you attempt to modify the state of a component (Bookings) which is mostly the parent component, while it's in the process of rendering another component (BookingConfirmationModal) which is children component and you probably had passed a setState() function into it as a prop. However, This can lead to unexpected behavior and inconsistencies in your application's UI.

In this blog I will try to guide you through understanding this error, debugging its source, and implementing effective solutions to prevent it from occurring in your React projects again.

Understanding the Error

React's rendering process is designed to be efficient and predictable. When a component's state or props change, React initiates a re-rendering process. During this process, React traverses the component tree, updating and re-rendering components as needed.The core issue with the "Cannot update state while rendering" error lies in the violation of this predictable rendering order. When a component tries to modify the state of another component during its own rendering phase, it disrupts the rendering cycle and can lead to:

• Infinite Loops: The state updates trigger continuous re-renders, potentially crashing the application.
• Inconsistent UI: The UI may not reflect the intended state changes accurately.
• Data Races: Multiple components might attempt to modify the same state concurrently, leading to unpredictable outcomes.

Possible Causes

• State Update in Render Phase: The most likely cause is that you are calling setState inside the render method or during the rendering process of BookingConfirmationModal.

• Side Effects in Render: You might be performing side effects (like fetching data or updating state) directly in the render method, which should be avoided.

Solution

To fix this issue, you should ensure that state updates are not happening during the render phase! Here are a few steps you can take:

• Move State Updates to useEffect: If you need to update the state based on some condition, use the useEffect hook to perform the update after the component has rendered.

import React, { useEffect } from 'react';

const BookingConfirmationModal = ({ someProp }) => {
  useEffect(() => {
    // Perform state updates here
    // Example: setState(someValue);
  }, [someProp]); // Add dependencies if needed

  return (
    <div>
      {/* Your component JSX */}
    </div>
  );
};

• Avoid Direct State Updates in Render: Ensure that you are not calling setState directly within the render method or any function that is called during rendering.

• Check for Conditional State Updates: If you have conditional logic that updates the state, make sure it is not being executed during the render phase.

• Check your useMemo: If you have used useMemo incase, remove that and use useEffect instead in the child component so that it will run after the component mounts or move you useMemo to the parent component. That will solve the warning.

A possible solution would look like -

import { useState, useEffect } from "react";
import BookingConfirmationModal from "./BookingConfirmationModal";

function App() {
  const [showModal, setShowModal] = useState(false);
  // other code

  return (
    <div>
      <h1>This is app</h1>
      <button onClick={() => setShowModal(true)}>Show Modal</button>
      {showModal ? <Testing BookingConfirmationModal={setTestingState} /> : null}
    </div>
  );
}

export default App;

// BookingConfirmationModal.jsx
const BookingConfirmationModal= ({ setTestingState }) => {

  useEffect(()=> {
    setTestingState(false)
   }, [setIsModalVisible]) //or other required dependencies

  return (
    <div>
      <button onClick={() => setTestingState(false)}>Close Modal</button>
      // other codes
    </div>
  );
};

export default BookingConfirmationModal;

Happy coding!

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