comflow.js

// Com flow

import * as React from 'react';

type Props = {
  type: string,
  children: React.Node,
};

type State = {
  count: number,
};

export default class Button extends Component<Props, State> {
  state = {
    counter: 0,
  };

  updateCounter = () => {
    this.setState(state => ({ counter: state.counter + 1 }));
  };

  render() {
    return (
      <button onClick={this.updateCounter} type={this.props.type}>
        {this.props.children}
      </button>
    );
  }
}