var App = React.createClass({
  getInitialState: function() {
    return { a: 0, b: 0, c: 0 }
  },
  
  handleClick: function(btn, e) {
    this.setState({ 
      [btn]: this.state[btn] + 1
    });
  },
  
  render: function() {
    return <div>
      <button onClick={this.handleClick.bind(this, 'a')}>{this.state.a}</button>
      <button onClick={this.handleClick.bind(this, 'b')}>{this.state.b}</button>
      <button onClick={this.handleClick.bind(this, 'c')}>{this.state.c}</button>
    </div>
  }
});

ReactDOM.render(<App />, document.querySelector('main'));