为react组件库添加typescript类型提示的方法

import * as React from 'react';

interface CountdownProps {
  count?: number;
  dayText?: string | React.ReactElement;
  hourText?: string | React.ReactElement;
  minuteText?: string | React.ReactElement;
  secondText?: string | React.ReactElement;
  callback?: Function;
  className?: string;
  style?: React.CSSProperties;
  rest?: any
}

interface CountdownState {
  count?: number;
}

declare module 'react-better-countdown' {
  export default class Countdown extends React.Component<CountdownProps, CountdownState> {
    state: CountdownState;
    timer: null | number;
    tick: () => void;
    componentDidMount(): void;
    componentDidUpdate(prevProps: CountdownProps): void;
    componentWillUnmount(): void;
    render: () => React.ReactElement;
  }
}