title: Difference between this two reactjs setState behavior
body: <p>Here is some React/JS code:
  Is there a difference between:</p>
  <pre><code>setState({var1: ...., var2: ...}, this.callback_function);
  </code></pre>
  <p>and</p>
  <pre><code>setState({var1: ...., var2: ...});
  this.callback_function();
  </code></pre>
  <p>Thanks a lot</p>