What Are Controlled and Uncontrolled Components in React?

In React, understanding the difference between controlled and uncontrolled components can significantly impact the way you manage your application’s state and handle user inputs. Let’s delve into what these terms mean and the implications they have on React applications.

Controlled Components

Controlled components are those in which form data is handled by the React component itself. The component’s state is the single source of truth. When a user interacts with a controlled component, any change is immediately reflected in the React state. Updating the state triggers a re-render, ensuring that the UI and input fields are always in sync with the component state.

Advantages: - Greater control over form data. - Immediate validation and manipulation. - Improved data handling and consistency.

Example:

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class ControlledInput extends React.Component {
  constructor(props) {
    super(props);
    this.state = { value: '' };
  }

  handleChange = (event) => {
    this.setState({ value: event.target.value });
  };

  render() {
    return (
      <input type="text" value={this.state.value} onChange={this.handleChange} />
    );
  }
}

Uncontrolled Components

Uncontrolled components, on the other hand, rely on the DOM to manage form data. In these components, React doesn’t manage the form state; instead, DOM element maintains its own state internally. You access data using refs, which allows you to extract the input value anytime you need it.

Advantages: - Simpler to set up, particularly for simple forms or when migrating legacy code. - Less boilerplate code, as you don’t need to manage form state in React.

Example:

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class UncontrolledInput extends React.Component {
  constructor(props) {
    super(props);
    this.inputRef = React.createRef();
  }

  handleSubmit = (event) => {
    console.log(this.inputRef.current.value);
    event.preventDefault();
  };

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <input type="text" ref={this.inputRef} />
        <button type="submit">Submit</button>
      </form>
    );
  }
}

Key Considerations

• Performance: Controlled components can lead to more renders as the state is updated with every keystroke. For complex forms, use controlled components selectively to avoid performance bottlenecks.
• Complexity: Controlled components offer more control, which can make them more complex to set up, especially for forms with lots of inputs.
• Validation: Immediate validation and feedback are easier to implement with controlled components due to the state driven nature.

Learn More

For further reading on managing state in React applications, you may explore these articles:

• React.js: Learn how to handle scripts and run applications efficiently.
• React.js Hosting: Discover tips on hosting your React applications.
• React.js Deployment: Get insights into deploying React applications effectively on an Ubuntu server.

By understanding and choosing between controlled and uncontrolled components, developers can create React apps that are both performant and aligned with design intentions.