counter.jsx

counter.js

"use strict";

var Counter = React.createClass({
  displayName: "Counter",

  incrementCount: function incrementCount() {
    this.setState({count: this.state.count + 1});
  },
  getInitialState: function getInitialState() {
    return {
      count: 0
    };
  },
  render: function render() {
    return React.createElement( "div", {
      "class": "my-component" },
      React.createElement("h1", null, "Count: ", this.state.count),
      React.createElement("button", { type: "button", onClick: this.incrementCount }, "Increment"
    ));
  }
});

React.render(React.createElement(Counter, null), document.getElementById('mount-point'));

counter.jsx

var Counter = React.createClass({
  incrementCount: function(){
    this.setState({
      count: this.state.count + 1
    });
  },
  getInitialState: function(){
     return {
       count: 0
     }
  },
  render: function(){
    return (
      <div class="my-component">
        <h1>Count: {this.state.count}</h1>
        <button type="button" onClick={this.incrementCount}>Increment</button>
      </div>
    );
  }
});

React.render(<Counter/>, document.getElementById('mount-point'));

test.html

<div id="mount-point"></div>