title: (React) Dynamic dropdown box examples. HowTo?
body: <p>Can anyone point me in the direction of any dynamic React drop-down box examples? </p>
  
  <p>I wish to implement drop-down functionality, which will take the result of a primary drop-down selection, to determine the output of a secondary drop-down list. For example, selecting 'London' from a primary drop-down list, will populate a secondary drop-down box with regions (boroughs) within London. </p>
  
  <p>I'm planning to populate the drop-down boxes by selecting data from a firebasedb.</p>