React ViewportInfo component

viewport-info.jsx

var ViewportInfo = React.createClass({

  getInitialState: function () {
    return {
      width: null,
      height: null
    };
  },

  componentDidMount: function () {
    this.getWindowDimensions();
    window.addEventListener("resize", this.getWindowDimensions);
  },

  componentWillUnmount: function () {
    window.removeEventListener("resize", this.getWindowDimensions);
  },

  getWindowDimensions: function () {
    this.setState({
      width: window.innerWidth,
      height: window.innerHeight
    });
  },

  render: function () {
    return (
      <div>
        <span>{this.state.width}</span> &times; <span>{this.state.height}</span>
      </div>
    );
  }
});