title: Call custom method on component when props update
body: <p>I have a <code>YouTubeiFrame</code> react component that renders an empty div and then drops the YouTube iframe player in to that div using <code>componentDidMount</code>. All works fine. I have a <code>cueVideo</code> method defined on the component which uses the players
  API to cue new videos:</p>
  
  <pre><code>cueVideo(videoId) {
    this.player.cueVideoById(videoId)
  }
  </code></pre>
  
  <p>In different places in my app you can click a button or some another action to indicate that you  want to play a new video. When you perform this action the 'currentVideo' state is updated via redux and as a result the YouTubeiFrame component receives the new video id as an updated prop. </p>
  
  <p>My question is how to call the <code>cueVideo</code> method above in reaction to the updated prop. I've considered using <code>shouldComponentUpdate</code> to compare <code>this.props.currentVideo</code> with the next props 
  but concious this method is really supposed to return true/false so the render function can be called. All I want to do is call <code>cueVideo</code> when the currentVideo prop changes - I don't really need to re-render.</p>
  
  <p>What's the best way to do this?</p>