how to use refs in functional component react js code example

Example 1: when to use react ref

WHEN TO USE REACT'S REF ATTRIBUTE?
But it is not always a good idea to use the ref attribute. The general rule of thumb is to avoid it. The official React documentation mentions three occasions where you can use it because you have no other choice.

Managing focus, text selection, or media playback.
Integrating with third-party DOM libraries.
Triggering imperative animations.

Example 2: use ref in component reactjs

class CustomTextInput extends React.Component {
  constructor(props) {
    super(props);
    // Crée une référence pour stocker l’élément DOM textInput
    this.textInput = React.createRef();    this.focusTextInput = this.focusTextInput.bind(this);
  }

  focusTextInput() {
    // Donne explicitement le focus au champ texte en utilisant l’API DOM native.
    // Remarque : nous utilisons `current` pour cibler le nœud DOM
    this.textInput.current.focus();  }

  render() {
    // Dit à React qu’on veut associer la ref `textInput` créée
    // dans le constructeur avec le `<input>`.
    return (
      <div>
        <input
          type="text"
          ref={this.textInput} />        <input
          type="button"
          value="Donner le focus au champ texte"
          onClick={this.focusTextInput}
        />
      </div>
    );
  }
}