title: ReactJS State and Local Variable
body: <p>Ref:
  ReactJS documents page URL: <a href="https://facebook.github.io/react/docs/state-and-lifecycle.html" rel="noreferrer">https://facebook.github.io/react/docs/state-and-lifecycle.html</a></p>
  
  <p>Is <i><b>timerID </b></i>in the assignment <i>this.timerID = setInterval</i> just a variable. Why is this not a <i>state</i>?</p>