求助：React--es6，ref回调函数无法获取dom节点问题

Question

问题：imgDom.scrollWidth = NAN;
代码：

class imgF extends React.Component {
    render() {
        return (
            <figure>
                <img/>
                //图片显示正常
                <h2></h2>
            </figure>
        )
    }
}



class App extends React.Component{
    componentDidMount(){

    ......

        let imgDom = this.img0,
            imgW = imgDom.scrollWidth;
            //问题：imgW is NAN...

    ......

    }

    render() {

        ......

        let imgs = [];
        for(let i = 0; i < 10; i++){
            imgs.push(<imgF key={'img' + i} ref={(imgf) => {this['img' + i] = imgf}}/>
        }

        return (
            <section>
                {imgs}
            </section>
        )
    }
}