How can I attach to a stateless component's ref in React?

Question

I am looking to create a stateless component who's input element can be validated by the parent component.

In my example below, I am running into a problem where the input ref is never being assigned to the parent's private _emailAddress property.

When handleSubmit is called, this._emailAddress is undefined. Is there something I'm missing, or is there a better way to do this?

interface FormTestState {
    errors: string;
}

class FormTest extends React.Component<void, FormTestState> {
    componentWillMount() {
        this.setState({ errors: '' });
    }

    render(): JSX.Element {
        return (
            <main role='main' className='about_us'>             
                <form onSubmit={this._handleSubmit.bind(this)}>
                    <TextInput 
                        label='email'
                        inputName='txtInput'
                        ariaLabel='email'
                        validation={this.state.errors}
                        ref={r => this._emailAddress = r}
                    />

                    <button type='submit'>submit</button>
                </form>
            </main>
        );
    }

    private _emailAddress: HTMLInputElement;

    private _handleSubmit(event: Event): void {
        event.preventDefault();
        // this._emailAddress is undefined
        if (!Validators.isEmail(this._emailAddress.value)) {
            this.setState({ errors: 'Please enter an email address.' });
        } else {
            this.setState({ errors: 'All Good.' });
        }
    }
}

const TextInput = ({ label, inputName, ariaLabel, validation, ref }: { label: string; inputName: string; ariaLabel: string; validation?: string; ref: (ref: HTMLInputElement) => void }) => (
    <div>
        <label htmlFor='txt_register_first_name'>
            { label }
        </label>

        <input type='text' id={inputName} name={inputName} className='input ' aria-label={ariaLabel} ref={ref} />

        <div className='input_validation'>
            <span>{validation}</span>
        </div>
    </div>
);

Answer 1

EDIT: You now can with React Hooks. See the answer by Ante Gulin.

You can't access React like methods (like componentDidMount, componentWillReceiveProps, etc) on stateless components, including refs. Checkout this discussion on GH for the full convo.

The idea of stateless is that there isn't an instance created for it (state). As such, you can't attach a ref, since there's no state to attach the ref to.

Your best bet would be to pass in a callback for when the component changes and then assign that text to the parent's state.

Or, you can forego the stateless component altogether and use an normal class component.

From the docs...

You may not use the ref attribute on functional components because they don't have instances. You can, however, use the ref attribute inside the render function of a functional component.

function CustomTextInput(props) {
  // textInput must be declared here so the ref callback can refer to it
  let textInput = null;

  function handleClick() {
    textInput.focus();
  }

  return (
    <div>
      <input
        type="text"
        ref={(input) => { textInput = input; }} />
      <input
        type="button"
        value="Focus the text input"
        onClick={handleClick}
      />
    </div>
  );  
}

Answer 2

You can useuseRef hook which is available since v16.7.0-alpha.

EDIT: You're encouraged to use Hooks in production as of 16.8.0 release!

Hooks enable you to maintain state and handle side effects in functional components.

function TextInputWithFocusButton() {
  const inputEl = useRef(null);
  const onButtonClick = () => {
    // `current` points to the mounted text input element
    inputEl.current.focus();
  };
  return (
    <>
      <input ref={inputEl} type="text" />
      <button onClick={onButtonClick}>Focus the input</button>
    </>
  );
}

Read more in Hooks API documentation

Answer 3

The value of your TextInput is nothing more than a state of your component. So instead of fetching the current value with a reference (bad idea in general, as far as I know) you could fetch the current state.

In a reduced version (without typing):

class Form extends React.Component {
  constructor() {
    this.state = { _emailAddress: '' };

    this.updateEmailAddress = this.updateEmailAddress.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  updateEmailAddress(e) {
    this.setState({ _emailAddress: e.target.value });
  }

  handleSubmit() {
    console.log(this.state._emailAddress);
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <input
          value={this.state._emailAddress}
          onChange={this.updateEmailAddress}
        />
      </form>
    );
  }
}