How to connect an event to a button by class name?

Question

JavaScript

A script with an onClick event was written in react, js was compiled.
The question is how to implement an event for buttons by class name, but without creating the buttons themselves through a script.
Now it looks like this, and inside the buttons with the class name booking, other buttons are created, to which the event is set.

var App = React.createClass({
    getInitialState() {
        return { smShow: false};
    },

    showModal() {
        this.setState({show: true});
    },

    hideModal() {
        this.setState({show: false});
    },

    render() {
        let smClose = () => this.setState({ smShow: false });

        return (
            <ButtonToolbar>
                <Button bsStyle="primary" onClick={()=>this.setState({ smShow: true })}>
                    Contact Form
                </Button>

                <MySmallModal show={this.state.smShow} onHide={smClose}/>
            </ButtonToolbar>
        );
    }
});

ReactDOM.render(<App />, document.getElementById('booking'));

Answer 1

so does not roll?

componentDidMount(){
  var btns = document.querySelectorAll('.btn');
    for (var i = 0; i < btn.length; i++) {
        btn[i].addEventListener("click",()=>this.setState({ smShow: true }));
    }
}