class App extends React.Component {
  
  state = {
    result: '',
    entry1: '',
    entry2: ''
  }

  handleEntry1 = (event) => {
    this.setState({entry1: event.target.value})
  }
  
    handleEntry2 = (event) => {
    this.setState({entry2: event.target.value})
  }

  handleAddition = (event) => {
    const firstInt = parseInt(this.state.entry1)
    const secondInt = parseInt(this.state.entry2)
    this.setState({result: firstInt + secondInt })
  }
  
  render() {
    const { entry1, entry2, result } = this.state
    return(
      <div>  
        <div>
          Result: { result }
        </div>
        <span><input type='text' onChange={this.handleEntry1} /></span>
        <br />
        <br />
        <span><input type='text' onChange={this.handleEntry2} /></span>
        <div>
          <button onClick={this.handleAddition} type='submit'>Add</button>
        </div>
      </div>
    )
  }
}

ReactDOM.render(<App />, document.getElementById("root"));