getDerivedStateFromProps

getDerivedStateFromProps is a static method in React class components that enables the component to update its state based on changes in props. It's invoked right before calling the render method, both on the initial mount and on subsequent updates. It should return an object to update the state, or null to indicate that the new props do not require any state updates.

Here's the method signature:

```jsx
static getDerivedStateFromProps(props, state)
```

Here is a simple example:

```jsx
class ExampleComponent extends React.Component {
state = {
someStateValue: '',
};

static getDerivedStateFromProps(props, state) {
if (props.somePropValue !== state.someStateValue) {
return {
someStateValue: props.somePropValue,
};
}
// Return null if the state hasn't changed
return null;
}

render() {
// Render something based on the state
}
}
```

In this example, whenever the prop `somePropValue` changes and it's different from the current state value `someStateValue`, the component's state is updated to reflect this change. If the prop value hasn't changed, the method returns null and the state remains the same. This allows the component to have its state derived from its props, hence the name `getDerivedStateFromProps`.

However, React documentation suggests avoiding `getDerivedStateFromProps` if possible, in favor of simpler alternatives such as `componentDidUpdate` lifecycle method or memoization helpers. The reason is because this method could lead to bugs and inconsistencies if not used properly.