title: React router POP
body: <p>I'm investigating my react application's router actions history, and found that there are many "POP" action that comes right after a "REPLACE" action. I couldn't seem to find more documentation about the "POP" action, what is it? and what does it do?</p>
  
  <p>Is it safe or right to add a validation in my component to validate the <code>location.action</code> in my <code>componentDidUpdate()</code> life cycle?</p>
  
  <p><a href="https://i.stack.imgur.com/BJvwM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BJvwM.png" alt="enter image description here"></a></p>