Listeners are components in React that allow you to subscribe to changes in the state of a component. When the state of the component changes, the listener will be called with the new state as an argument.

Listeners are useful for when you want to update the UI of a component based on changes in the state of another component. For example, you could have a listener in a child component that updates its UI based on changes in the state of its parent component.

Here is an example of how to use a listener in React:

```jsx

import React, { useState } from 'react';

const ParentComponent = () => {

const [count, setCount] = useState(0);

return (

);

};

const ChildComponent = ({ count }) => {

useEffect(() => {

// This function will be called every time the `count` prop changes

console.log(`Count changed to ${count}`);

}, [count]);

return (

);

};

export default ParentComponent;

```

In this example, the `ChildComponent` has a listener that is called every time the `count` prop changes. The listener logs the new count to the console.