counter-class.tsx

import React, { Component } from 'react'

interface Props {
  initialCount: number
}

interface State {
  count: number
}

class CounterClass extends Component<Props, State> {
  constructor(props: Props) {
    super(props)
    const { initialCount } = props
    this.state = {
      count: initialCount
    }
    this.increment = this.increment.bind(this)
  }

  increment() {
    this.setState({ count: this.state.count + 1 })
  }

  render() {
    const { count } = this.state
    return (
      <button onClick={this.increment}>{count}</button>
    )
  }
}

export default CounterClass