shouldComponentUpdate is a lifecycle method in class-based React components that lets you control whether a component should re-render or not.

How it works:

• When a component’s state or props change, shouldComponentUpdate(nextProps, nextState) is called.
• By default, it returns true (always re-render).
• You can override it to return false if the new props or state do not affect the output, preventing unnecessary re-render.

Example:

class MyComponent extends React.Component {
  shouldComponentUpdate(nextProps, nextState) {
    return nextProps.value !== this.props.value;
  }

  render() {
    console.log('Rendering...');
    return <div>{this.props.value}</div>;
  }
}

In this case, the component will only re-render if the value prop actually changes.

Tips:

• Be careful with complex props like objects and arrays — they may need deep comparison.
• For simple components, you can extend React.PureComponent instead of manually writing shouldComponentUpdate. PureComponent does shallow comparison automatically.

PureComponent Example:

class MyComponent extends React.PureComponent {
  render() {
    return <div>{this.props.value}</div>;
  }
}

Summary:
Use shouldComponentUpdate (or PureComponent) to manually control re-renders and boost performance in class components. In functional components, you can achieve similar results using React.memo.

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