JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/prop-types@15.5.10/prop-types.js"></script>
<script src="https://unpkg.com/react@15.6.2/dist/react-with-addons.js"></script>
<script src="https://unpkg.com/react-dom@15.6.2/dist/react-dom.js"></script>
<div id="container"></div>

Babel + JSX

class ControlledSelect extends React.Component {
  render() {
    console.log(this.props.items);

    return (
      <select
        onChange={(evt) => this.props.onChange(evt.target.value)}
      >
        {Object.entries(this.props.items)
          .map(([value, isSelected]) => (
            <option key={value} value={value}>
              {isSelected && '(Y) '}
              {value} 
              {'Some string'}
            </option>
          ))}
      </select>
    )
  }
}


class App extends React.Component {
  state = {
    items: {
      a: false,
      b: false,
    }
  }

  render() {
    return (
      <ControlledSelect 
        items={this.state.items} 
        onChange={v => {
          this.setState({
            items: {
              ...this.state.items,
              [v]: true,
            }
          });
        }}
      />
    )
  }
}


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