title: react js , get siblings or parent value
body: <p>I'm new to react, I'm curious how to do this properly.
  suppose I have this form, by clicking button, I want to get textbox value,</p>
  
  <pre><code>var form = React.createClass({
     submit : function(e){
        //how to get textbox value?
     },
     render : function(){
     return (
        &lt;form&gt;
           &lt;input type="text" id="textbox" value="hey, get me"/&gt;
           &lt;button onClick={this.submit}&gt;Get it&lt;/button&gt;
        &lt;/form&gt;
        );
     }
  });
  </code></pre>
  
  <p>Any answer will be appreciated! thank you!</p>