Button counter react

JavaScript
1
  1. What I do not understand about the below, what is wrong with just writing this.updateButton1 why do I have to add .bind(this) how does this make sense that in order to get it to work you have to bind this to this? bind this to itself?
  2. Under updatebutton Why does it not work when just doing +1 why does it have to be +=1
class Buttons extends React.Component {
  state = {clicks1: 0, clicks2: 0};

  updateButton1() {
    this.setState((prevState) => {
      clicks1: prevState.clicks1 += 1
    });
  }

  updateButton2() {
    this.setState((prevState) => {
      clicks2: prevState.clicks2 += 1
    });
  }

  render() {
    return (
      <div>
        <button onClick={this.updateButton1.bind(this)}>{this.state.clicks1}</button>
        <br/><br/>
        <button onClick={this.updateButton2.bind(this)}>{this.state.clicks2}</button>
      </div>
    )
  }
}

//"inject" to DOM
ReactDOM.render(
  <Buttons/>,
  document.getElementById('buttons')
);