title: What do parameters of React.Component.setState() mean syntactically?
body: <p>Currently I'm reading the documentation of React and I don't understand what do the following parameters mean syntactically in <a href="https://reactjs.org/docs/react-component.html#setstate" rel="nofollow noreferrer"><code>setState()</code></a> method:</p>
  
  <pre><code>setState(updater[, callback])
  </code></pre>
  
  <p>I tried to use <a href="http://esprima.org/demo/parse.html?code=setState(updater%5B%2C%20callback%5D)" rel="nofollow noreferrer">Esprima parser</a> to perform syntatical analysis in order to determine what are those but it shows syntactical error for the line of code.</p>