title: Value of this in React event handler
body: <p>For some reason the value of this is being lost in react event handler. Reading the docs I thought that react did some stuff here to make sure this was set to the correct value</p>
  
  <p>The following doesn't work as I'd expect</p>
  
  <pre><code>import React from 'react';
  
  export default class Observer extends React.Component {
  
      handleClick() {
          console.log(this); //logs undefined
      }
      render() {
          return (
              &lt;button onClick={this.handleClick}&gt;Click&lt;/button&gt;
          );
      }
  }
  </code></pre>
  
  <p>But this does:</p>
  
  <pre><code>import React from 'react';
  
  export default class Observer extends React.Component {
  
      handleClick() {
          console.log(this); //logs Observer class instance
      }
      render() {
          return (
              &lt;button onClick={this.handleClick.bind(this)}&gt;Click&lt;/button&gt;
          );
      }
  }
  </code></pre>
  
  <p>React and ES6 is new to me but this seems to not be the correct behaviour?</p>