title: Reactjs - value undefined
body: <p>First of all, I suspect that const vector object is probably in a wrong place but I don't know where to put it.
  I'm trying to control the position of the SVG object with arrow keys. It does not seem to be able to access x.</p>
  
  <pre><code>class Circle extends React.Component {
    render() {
      const { h, w, x, y, r, stroke, fill } = this.props;
      return (
        &lt;svg height={h} width={w}&gt;
          &lt;circle cx={x} cy={y} r={r}
            stroke={stroke} strokeWidth="3" fill={fill} 
          /&gt;
        &lt;/svg&gt; 
      )
    }
  }
  
  class App extends React.Component {
    constructor(props) {
      super(props)
      this.state = {
        h: 100,
        w: 500,
        x: 50,
        y: 50,
        r: 40,
        stroke: "black",
        fill: "red"
      }
    }
    _currentPosition() {
      // Display the current position
      console.log(this.state.x, this.state.y);
    }
  
    _handleKey(e){
      // Define key codes and movement vectors
      const vector = {
          37: [-10, 0],
          38: [0, -10],
          39: [10, 0],
          40: [0, 10]
      };
      // Display the current position
      this.currentPosition;
  
      // Detect key presses and change the position accordingly
        if (e.keyCode in vector) {
        this.setState({
          x: this.state.x + vector[e.keyCode][0],
          y: this.state.y + vector[e.keyCode][1]
        })
          } 
    }
  
     componentDidMount() {
       document.addEventListener("keydown", this._handleKey, false);
    }
     render() {
      return (
        &lt;div&gt;
        &lt;Circle { ...this.state } onKeyPress={this.handleKeyPress}/&gt;
        &lt;/div&gt;
      )
    }
  }
  
  ReactDOM.render(&lt;App /&gt;, document.getElementById('app'))
  </code></pre>
  
  <p>I have got the error:</p>
  
  <pre><code>VM211 pen.js:76Uncaught TypeError: Cannot read property 'x' of undefined
  _handleKey @ VM211 pen.js:76
  </code></pre>
  
  <p>The code it is:
  <a href="http://codepen.io/wasteland/pen/GZvWeo?editors=0110" rel="nofollow">http://codepen.io/wasteland/pen/GZvWeo?editors=0110</a></p>
  
  <p>Thank you</p>