React offers two primary ways to handle form elements—Controlled Components and Uncontrolled Components. Understanding the internal behavior and ideal use cases of each is essential for managing user input efficiently in React applications.

1. What is a Controlled Component?

A controlled component is one where the form element’s value is bound to React state. The component does not manage its own state; instead, every user input is immediately captured by React through an event handler and stored using useState (or class component’s this.state).

Detailed Characteristics:

• React state holds the form data: The form’s input values are stored in React’s memory using useState, making them predictable and trackable.
• Changes trigger state updates: As the user types or interacts with the input field, the onChange handler is invoked, updating the state using setState.
• The input element’s value is controlled by React: The value prop of the input is explicitly set using a state variable. This means the form field reflects whatever the React state contains.
• Ideal for validations and dynamic behavior: Because you control the value via state, you can instantly validate or transform the input, enable/disable buttons, or implement live character counters.

Controlled Component Example

import React, { useState } from "react";

function ControlledForm() {
  const [name, setName] = useState("");

  const handleChange = (event) => {
    setName(event.target.value); // Update state on each keystroke
  };

  const handleSubmit = (event) => {
    event.preventDefault(); // Prevents page reload
    alert(`Submitted name: ${name}`);
  };

  return (
    <form onSubmit={handleSubmit}>
      <label>
        Name:
        <input type="text" value={name} onChange={handleChange} />
      </label>
      <button type="submit">Submit</button>
    </form>
  );
}

2. What is an Uncontrolled Component?

An uncontrolled component is one where the DOM itself manages the form element’s state, and React accesses the current value only when needed, using the ref API. This mimics the traditional approach of form handling in plain HTML and JavaScript.

Detailed Characteristics:

• State is managed by the input element itself: The input field internally keeps track of what the user types. React does not intervene during each change.
• React uses a ref to read the value when needed: When the form is submitted or accessed, you use a reference (useRef) to directly read the value from the DOM element.
• Better performance for simple use cases: Since React does not re-render on every keystroke, this approach avoids unnecessary rendering and may be more performant in simple or static forms.
• Less code for simple forms: You don’t need to write an onChange handler or maintain state for every input, which keeps the code concise for one-off value collection.

Uncontrolled Component Example

import React, { useRef } from "react";

function UncontrolledForm() {
  const nameRef = useRef(); // Create a reference to the input element

  const handleSubmit = (event) => {
    event.preventDefault();
    alert(`Submitted name: ${nameRef.current.value}`); // Access value directly from the DOM
  };

  return (
    <form onSubmit={handleSubmit}>
      <label>
        Name:
        <input type="text" ref={nameRef} />
      </label>
      <button type="submit">Submit</button>
    </form>
  );
}

Feature-by-Feature Comparison

Feature	Controlled Component	Uncontrolled Component
Data Source	React state (useState or this.state in class components). React is the source of truth for the input value.	DOM input field manages its own state internally.
Change Handling	Requires an onChange event handler to sync the state and input field.	No need for onChange; value can be read on demand using ref.
Form Initialization	Initial value is set with a useState variable or value prop.	Initial value is set with defaultValue prop or hardcoded directly in the HTML element.
Validation	Real-time validation is possible during user input. You can provide dynamic feedback like errors or styling.	Validation needs to be done after reading the value using ref, typically on form submission.
React Integration	Fits seamlessly with other React state logic, making dynamic behavior easier to implement.	Less integrated with React; best for simpler forms or when using third-party DOM libraries.
Performance	Slightly more rendering overhead due to re-renders on every input update.	Better for performance in large static forms as there’s no state update on each input change.
Best Use Case	Complex forms, conditional rendering, live feedback, dynamic rules or multi-step wizards.	Simple forms, integrations with non-React libraries, or when collecting data only at submission time.

Best Practices

Controlled Components:

• Always define an onChange handler for each controlled input.
• Use controlled components when you need real-time feedback, form validation, or to toggle button states conditionally.
• Avoid mixing value and defaultValue — using both inappropriately can lead to confusing bugs.

Uncontrolled Components:

• Use useRef responsibly to avoid over-reliance on reading from the DOM, which breaks the declarative nature of React.
• Avoid complex logic with uncontrolled inputs. It’s harder to integrate them into dynamic or conditionally rendered components.
• Best for simple forms, third-party UI libraries (like jQuery), or performance-sensitive applications.

Conclusion

Understanding the difference between controlled and uncontrolled components helps you choose the right tool for the job:

• Use Controlled Components when you need full control, validation, and live feedback.
• Use Uncontrolled Components when you need simplicity, better performance, or are integrating with traditional HTML or external JS libraries.