title: Modify a href link value based on mobile OS
body: <p>I want to read the OS of the system the user is browsing and offer him the relevant kind of redirect to the App store or Google Play.</p>
  
  <p>If the user clicks on the app icon in my website it would be redirected to the appropriate store based on the device.</p>
  
  <p>I believe i can read the OS using javascript and the if function but i don't know how to append the actual url that sits behind the  tag.</p>