title: getElementById in React
body: <p>Getting this error at the moment:</p>
  
  <p><code>Uncaught TypeError: Cannot read property 'value' of null</code></p>
  
  <p>I call this in my render function below:</p>
  
  <pre><code>&lt;input type="submit" className="nameInput" id="name" value="cp-dev1" onClick={this.writeData}/&gt;
  </code></pre>
  
  <p>I also have tried calling it in here</p>
  
  <pre><code>componentWillMount: function(){
          var name = document.getElementById('name').value;
        },
  </code></pre>
  
  <p>How can I get the id of an input text field and read that value and ensure it is not null?</p>
  
  <p>I think the DOM is loading after I try to read the element hence why it is null</p>