title: use of ''Getuserconfirmation" in react router v4
body: <p>use of ''Getuserconfirmation" in react router v4. What is the use of it, with this and without this difference ?</p>
  
  <pre><code>const callbacks = (data) =&gt; {
    console.log("callback consoled");
  }
  
  const getConfirmation = (message, callback) =&gt; {
    console.log('heyyy');
  const allowTransition = window.confirm(message)
    callbacks(allowTransition)
  }
  
  class App extends React.Component {
   render(){
      return(
          &lt;Router getUserConfirmation={getConfirmation}&gt;
          &lt;div&gt;
              &lt;Link exact to = "/"&gt;home&lt;/Link&gt;
              &lt;Link to = "/men"&gt;men&lt;/Link&gt;
              &lt;Link to = "/women"&gt;women&lt;/Link&gt;
          &lt;/div&gt;
          &lt;/Router&gt;
      );
    }
   }
  </code></pre>