Introduction to the React Ref System

Matthew Garcia

While React’s virtual DOM elegantly handles most situations you’ll run into, there are some cases where you’ll need to interact with the actual elements. For these occasions, React provides a ref system.

Creating a Ref

Creating a ref is pretty straightforward; just pass a callback that assigns to a property.

class MyComponent extends Component {
  render() {
    return (
      <div>
        <input ref={input => this.myInput = input} />
      </div>
    );
  }
}

From there, you can access that element via this.myInput. There are a few ways you can use this.

Using Refs to Get the Value of an Input

It’s as simple as accessing the value of the element. It’s like it’s 2005 again.

class MyComponent extends Component {
  alertInput() {
    const value = this.myInput.value;
    // Please don't use alert in actual applications.
    alert(value);
  }

  render() {
    return (
      <div>
        <input ref={input => this.myInput = input} />
        <button onClick={this.alertInput.bind(this)}>Alert</button>
      </div>
    );
  }
}

If you're using Redux, you'd probably want to use a controlled component for this. But it's handy to know for a quick demo.

Setting value won't end well; React will wipe out the element when it re-renders.

Using Refs to Focus Input

Managing focus is probably one of the most common use cases for refs, if only because there’s no good alternative.

class MyComponent extends Component {
  // As soon as the component mounts, `myInput` will be focused.
  componentDidMount() {
    this.myInput.focus();
  }

  render() {
    return (
      <div>
        <input ref={input => this.myInput = input} />
      </div>
    );
  }
}

Using Refs to Manipulate a Canvas

Canvases aren’t very useful unless there’s a canvas element with which to interact.

class MyComponent extends Component {
  // The canvas is drawn when the component is mounted.
  componentDidMount() {
    this.drawCanvas();
  }

  // The canvas is drawn when the component updates.
  componentDidUpdate() {
    this.drawCanvas();
  }

  drawCanvas() {
    const context = this.myCanvas.getContext('2d');
    context.clearRect(0, 0, 500, 500);
    context.fillText('If you can read this, your eyes are better than mine.', 250, 250);
  }

  render() {
    return (
      <div>
        <canvas ref={canvas => this.myCanvas = canvas} height={500} width={500} />
      </div>
    );
  }
}

Remember to redraw the canvas on update.

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