What is a controlled component?
In the context of React, a controlled component is one where the state of the form elements is managed by the component’s state. Rather than allowing the DOM to inherently handle the form inputs’ state, React takes control, ensuring a single source of truth and a consistent data flow within the application.
The core principle behind controlled components is that every change to the input is captured by a function, typically an event handler, and then the component’s state is updated with this new value. This updated state then determines the value of the input. By connecting the form element’s value directly to the React state, you ensure that the displayed value and the state value are always in sync. This relationship is established using the `value` prop for form elements like text inputs, and the `checked` prop for checkboxes and radio buttons.
An immediate advantage of this approach is predictability. Since the form’s data resides in the component’s state, it can be easily accessed, validated, or manipulated before submission. Furthermore, it provides more granular control over user interactions, such as conditionally allowing input changes or dynamically updating other UI elements based on input values.
While controlled components might initially seem verbose, especially for simple forms, their real power shines in more complex scenarios. Whether you’re creating dynamic forms, integrating real-time validations, or managing dependencies between different form elements, the controlled approach offers unparalleled precision and flexibility.
A controlled component in React is about establishing a firm bond between the component’s state and its form elements, championing a design where React, rather than the DOM, dictates the data flow and user experience.