문제 코드

class App extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            status: "No"
        };
    }
    changeState() {
        this.setState({ status: "Yes" });
    }
    render() {
        return (
            <div>
                <button onClick={ this.changeState }>Change!</button>
                <div>{this.state.status}</div>
            </div>
        );
    }
}

해결책

<button onClick={ this.changeState.bind(this) }>Change!</button>

원인