● Events in React JS allow developers to respond to user interaction within their applications quickly and efficiently. 
● Events are triggered whenever certain actions occur – from clicks to key presses - which then fire off callback functions so that appropriate responses can be made accordingly. 
● In React, events are handled using event handlers. An event handler is a function that is called when an event occurs. 
● Event handlers can be added to elements using the on[event] syntax, where [event] is the name of the event you want to handle. 
● For example, the onClick event handler is used to handle click events. It is important to note however that event handlers should always be set up correctly, so they do not get called unnecessarily which could lead to performance issues down the line. 
● Furthermore, events can also be used for more advanced tasks such as implementing drag-and-drop functionality or customizing how elements behave based on specific conditions like hover states etc., allowing developers even greater control over their UIs with minimal effort. 

Here is an example of a button that has an on click event handler: 

import React, { Component } from 'react'; 
class MyButton extends Component { 
handleClick = () => { 
console. log('Button clicked'); 
} 
render() { 
return <button onClick={this.handleClick}>Click me</button>; 
} 
} 
export default MyButton; 

In this example, the button has an onClick event handler that is set to the handleClick method. When the button is clicked, the handleClick method is called and the string "Button clicked" is logged to the console. 

React also has built-in events to handle common interactions such as onMouseEnter, onChange, onFocus, onBlur, onKeyDown, onKeyUp, onSubmit, etc.