import React from 'react';
import M from 'materialize-css';
....
// ref can only be used on class components
class SomeComponent extends Component {
  // get a reference to the element after the component has mounted
  componentDidMount(){
    M.Sidenav.init(this.sidenav);
  }

  render(){
    return (
      
 {this.sidenav = sidenav} }
          id={this.props.id}>
        // menuItems
      
    )
  }
}