⭐ Event Handler

camelCase로 사용

bind 해서 사용

/Event.js
class Toggle extends React.Component{
  constructor(props){
    super(props);
    this.state = {isToggleOn:true};
    **this.handleClick = this.handleClick.bind(this)**
  }

  handleClick(){
    this.setState(state=>({
      isToggleOn : !state.isToggleOn
    }))
  }
  render() {
    return (
      <button onClick={this.handleClick}>
        {this.state.isToggleOn ? 'ON':'OFF'}
      </button>
    );
  }}
  ReactDOM.render(
    <Toggle/>,
    document.getElementById('root')
  );

  export default Toggle