notification to download native app if accessing from mobile site

Question

I'm now creating a native app for blackberry, android, and iOS. I have a mobile site too that share the same functionality.

now I want everytime a user access the mobile site using specific device such as android or blackberry, it will give notification to download the app (redirect to bb app world or google play store). My reference here is just like the twitter mobile site, when you access it from blackberry, it will show you notification (with download link and 'x' button, just like from the image below). for now i'm thinking to use javascript detection, is it alright?

thanks.

*what i mean is that little block "New! Download the Twitter......"

Answer 1

From the other post:

    
      if( /Android|iPhone|BlackBerry/i.test(navigator.userAgent) ) {
      var url=confirm("Would you like to download our mobile application?");
        if (url==true)
      {
        var url = window.location.href = 'http://www.google.com';
        url.show(); 
      }
        else
      {

      }
      }