// App.jsx
// 其他代码省略
import './app.css';
<Animation isShow={isShow} name='demo'>
  <div class='demo'>
    demo
  </div>
</Animation>
// 通过改变isShow的值来指定是否显示
在 App.css 里指定进入离开效果：
// 基础样式
.demo {
  width: 200px;
  height: 200px;
  background-color: red;
}
// 定义进出入动画
.demo-showing {
  animation: show 0.5s forwards;
}
.demo-fading {
  animation: fade 0.5s forwards;
}
// 定义动画fade与show
@keyframes show {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}
@keyframes fade {
  from {
    opacity: 1;
  }
  to {
    opacity: 0;
  }
}

// Animation.jsx
import { PureComponent } from 'react';
import './index.css';
class Animation extends PureComponent {
  constructor(props) {
    super(props);
    this.state = {
      isInnerShow: false,
      animationClass: '',
    };
  }
  componentWillReceiveProps(props) {
    const { isShow } = props;
    if (isShow) {
      // 显示
      this.show().then(() => {
        this.doShowAnimation();
      });
    } else {
      // 隐藏
      this.doFadeAnimation();
    }
  }
  handleAnimationEnd() {
    const isFading = this.state.animationClass === this.className('fading');
    if (isFading) {
      this.hide();
    }
  }
  show() {
    return new Promise(resolve => {
      this.setState(
        {
          isInnerShow: true,
        },
        () => {
          resolve();
        }
      );
    });
  }
  hide() {
    this.setState({
      isInnerShow: false,
    });
  }
  doShowAnimation() {
    this.setState({
      animationClass: this.className('showing'),
    });
  }
  doFadeAnimation() {
    this.setState({
      animationClass: this.className('fading'),
    });
  }
  /**
   * 获取className
   * @param {string} inner 'showing' | 'fading'
   */
  className(inner) {
    const { name } = this.props;
    if (!name) throw new Error('animation name must be assigned');
    return `${name}-${inner}`;
  }
  render() {
    let { children } = this.props;
    children = React.Children.only(children);
    const { isInnerShow, animationClass } = this.state;
    const element = {
      ...children,
      props: {
        ...children.props,
        className: `${children.props.className} ${animationClass}`,
        onAnimationEnd: this.handleAnimationEnd.bind(this),
      },
    };
    return isInnerShow && element;
  }
}
export default Animation;