gistfile1.txt

class Canvas extends React.Component {
  componentDidMount() {
    this.props.draw(this.refs.a.getContext('2d'));
  }
  render() {
    const { width, height } = this.props;
    return <canvas ref='a' 
             width={width} 
             height={height}
             style={{width, height}}/>
  }
};


const draw = color => ctx => {

  ctx.fillStyle = 'black';
  ctx.fillRect(25,5, 40, 40);
  ctx.fillStyle = color;
  ctx.fillRect(20,0 , 40, 40);
    
};

<Canvas width={200} height={100} draw={draw('red')} />;
<Canvas width={200} height={100} draw={draw('#ffaa00')} />