What are Controlled and Uncontrolled form fields in React.js

Form elements in HTML, such as <input/>, <textarea>, <select>, and so on, often keep their inherent state and update it based on user input. We utilize state in every React component to make React apps interactive. The state of a component is initialized with a value and changed at some point in time based on user interactions with the application.

In React forms, input values are of two kinds, depending on your preference: uncontrolled and controlled inputs. To help you grasp the difference, we will go through both approaches to handling forms in React. The HTML technique, which utilizes "uncontrolled form fields," and the best practice, which utilizes "controlled form fields.”

Controlled Inputs

In controlled inputs, modifications and changes always occur in the form field.
This is seen in the value prop passed to the component. Every character typed, even something as simple as a backspace, counts as a change.
A significant part of a controlled component is that the state variable is the single source of truth.

We will utilize function components in this piece and React hooks. If you are not familiar with these concepts, do get acquainted with them.
Hooks, in a nutshell, are a cleaner, more succinct way of writing components. We will utilize a React Hook called useState() to build a function component. This hook exposes a state variable and a function to update the variable. Let’s have a code example:

    import React, { useState } from "react";

    function App (props) {
      const [message, updateMessage] = useState("");

        return (
          <div className="App" style={{ height: "20px" }}>
            <div className="container">
              <input
                type="text"
                placeholder="Enter message here.."
                value={message}
                onChange={(event) => updateMessage(event.target.value)}
              />
              <p>the message is: {message}</p>
            </div>
          </div>
        );
      };
    export default App;`

Here's a basic function component that renders a single input field on the page and reflects anything the user enters into it.

In the above function component called App, we have a state named message, and it can be updated using the updateMessage method. The input element returned in the component updates the state variable using its onChange event handler

A parent form element is not required for an input field to be classified as controlled..

It might be difficult to work with controlled components. If the page contains a large number of input elements, each one must be given a value property and an event handler.

View the full demo here

Uncontrolled Inputs

There is no updating or altering of states when the input values are uncontrolled. Uncontrolled components keep track of their internal state, which means the component remembers what you entered into the field. That value can be manipulated by utilizing the ref keyword to fetch it whenever it is needed. The value you submit is the value you get with uncontrolled inputs.

Refs allow you to access DOM nodes or React elements formed during the render process. More on refs

Uncontrolled components behave more like HTML form elements. The DOM, not the component, stores the data for each input element.

Let’s see an example below:

    import { useRef } from "react";
    const NameForm = () => {
      const inputRef = useRef(null);
      const handleSubmit = () => {
      alert(inputRef.current.value);
      };
      return (
      <div>
        <input type="text" placeholder="Type..." ref={inputRef} />
        <button onClick={handleSubmit}>Submit</button>
      </div>
      );
    };
    export default NameForm;

In the above example, we have created a ref called inputRef and attached it to the <input> element using ref attribute. Its value is displayed on the alert box upon clicking the submit button. View the full demo here

The next challenge on your mind might be when to use the controlled component and when to apply the uncontrolled component.

Working with controlled components on pages with numerous input fields might be problematic. An uncontrolled component is recommended in this scenario.
Controlled components are appropriate when handling form validations, as you can validate the input values on each keystroke.

Conclusion

Both controlled and uncontrolled form fields have their own set of advantages. Depending on the scenario, you may need to use both or one of them. If you're constructing a basic form with little to no UI feedback and no need for immediate validation (that is, you will only confirm and/or need the values after you submit), you should use uncontrolled inputs with refs. The source of truth would remain in the DOM, making it faster and requiring less code.

Controlled input is the way to go if you need more UI feedback and want to account for every minor change in a specific input field.