best-way.js

class AccessibleComponent extends Component {
  render() {
    return (
      <div>
        <div aria-label={this.props.label}>foo</div>
      </div>
    )
  }
}

better-way.js

class AccessibleComponent extends Component {
  render() {
    return (
      <div>
        <div aria-labelledby={() => this._label}>foo</div>
        <div ref={(c) => this._label = c}>bar</div>
      </div>
    )
  }
}