REACT Events

React provides a system to handle events in a similar way to DOM events in plain JavaScript. However, React events are not exactly the same as native DOM events. React wraps these events in its own event system called Synthetic Events, which ensures compatibility across all browsers.

1. What Are Events in React?

An event is an action or occurrence detected by the application, like clicking a button, hovering over an element, pressing a key, or submitting a form.

In React, you define event handlers as functions that get triggered when specific events occur.

2. Differences Between React and DOM Events

Feature React Events DOM Events
Naming CamelCase (e.g., onClick) Lowercase (e.g., onclick)
Event Handling Use functions directly Use strings or functions
Synthetic Events Uses Synthetic Events for compatibility Directly interacts with DOM
Default Behavior Prevented with event.preventDefault() Prevented with return false;

3. Adding Events in React

Example: Handling a Button Click

function App() {
    const handleClick = () => {
        alert('Button clicked!');
    };

    return (
        <button onClick={handleClick}>Click Me</button>
    );
}

export default App;

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  • onClick: React’s event handler for a click event.
  • The function handleClick is triggered when the button is clicked.

4. Passing Arguments to Event Handlers

You can pass arguments to event handlers using an arrow function or the .bind() method.

Example: Passing Arguments

function App() {
    const greet = (name) => {
        alert(`Hello, ${name}!`);
    };

    return (
        <button onClick={() => greet('John')}>Greet</button>
    );
}

export default App;

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Example: Using .bind()

function App() {
    const greet = (name) => {
        alert(`Hello, ${name}!`);
    };

    return (
        <button onClick={greet.bind(null, 'John')}>Greet</button>
    );
}

export default App;

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5. Common Event Types

React supports various event types. Below are some of the commonly used ones:

Event Type React Event Handler Example
Mouse Events onClick, onDoubleClick, onMouseOver, onMouseOut <button onClick={...}>
Keyboard Events onKeyDown, onKeyPress, onKeyUp <input onKeyDown={...}>
Form Events onChange, onSubmit, onFocus, onBlur <form onSubmit={...}>
Touch Events onTouchStart, onTouchMove, onTouchEnd <div onTouchStart={...}>
Clipboard Events onCopy, onCut, onPaste <input onPaste={...}>

6. Preventing Default Behavior

In React, you can prevent the default behavior of an event (e.g., preventing form submission) using event.preventDefault().

Example: Preventing Form Submission

function App() {
    const handleSubmit = (event) => {
        event.preventDefault(); // Prevent page reload
        alert('Form submitted!');
    };

    return (
        <form onSubmit={handleSubmit}>
            <input type="text" placeholder="Enter something" />
            <button type="submit">Submit</button>
        </form>
    );
}

export default App;

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7. Event Binding in Class Components

In class components, you may need to bind event handlers to the component’s context.

Example: Binding Event Handlers

import React, { Component } from 'react';

class App extends Component {
    constructor() {
        super();
        this.state = { count: 0 };
        this.increment = this.increment.bind(this); // Bind the method
    }

    increment() {
        this.setState({ count: this.state.count + 1 });
    }

    render() {
        return (
            <div>
                <p>Count: {this.state.count}</p>
                <button onClick={this.increment}>Increment</button>
            </div>
        );
    }
}

export default App;

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Alternatively, you can use an arrow function to avoid manual binding:

increment = () => {
    this.setState({ count: this.state.count + 1 });
};

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8. Handling Events in Loops

Example: Adding Click Events in Loops

function App() {
    const items = ['Apple', 'Banana', 'Cherry'];

    const handleClick = (item) => {
        alert(`You clicked: ${item}`);
    };

    return (
        <ul>
            {items.map((item, index) => (
                <li key={index} onClick={() => handleClick(item)}>
                    {item}
                </li>
            ))}
        </ul>
    );
}

export default App;

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9. Event Delegation

React uses a concept called event delegation to attach a single event listener at the root of the component tree. This improves performance compared to adding event listeners directly to DOM nodes.

10. Example: Complete Event Handling

function App() {
    const [text, setText] = useState('');
    const [submittedText, setSubmittedText] = useState('');

    const handleChange = (event) => {
        setText(event.target.value);
    };

    const handleSubmit = (event) => {
        event.preventDefault();
        setSubmittedText(text);
    };

    return (
        <div>
            <form onSubmit={handleSubmit}>
                <input type="text" value={text} onChange={handleChange} />
                <button type="submit">Submit</button>
            </form>
            {submittedText && <p>You submitted: {submittedText}</p>}
        </div>
    );
}

export default App;

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11. Best Practices for React Events

  1. Use Arrow Functions Wisely: Avoid defining arrow functions directly in JSX to prevent unnecessary re-renders.
  2. Clean Up Event Listeners: For custom or manual event listeners, always clean up in the useEffect cleanup function.
  3. Avoid Inline Functions in Loops: Use memoized callbacks with useCallback for performance optimization in complex components.

Conclusion

React events make handling user interactions simple and declarative.