title: Routing In Angular6
body: <p>I have application that have a navigation bar and in the navigation bar i have contactUs component.
  i can open the navigation bar from any of my componenets, and to go to contactUs component.
  in the contactUs  component i have a back button and i want to be able to take the user back from any component he opend the contactUs .
  how can i achieve this?</p>
  
  <p>i tried using routerLink on the button, and a navigatebyUrl with the router module but i only can take the user back from a specific url, like "/home"
  and i want it to be changes depends on the user location,
  e.g</p>
  
  <p>if user is open the 
  About > contactUs (so contactUs back button take back to About Component)
  Home > contactUs (so contactUs back button take back to Home Component)</p>
  
  <p>How can i achieve this approch?</p>