RxJs do operator on Observable

https://angularfirebase.com/lessons/methods-for-debugging-an-angular-application/

https://www.youtube.com/watch?time_continue=9&v=gxixM90vo9Y, around 5:32


this.db.object('items/12345/title')
           .do(val => console.log('before map', val) )
           .map(title => title.$value.toUpperCase() )
           .do(val => console.log('after map', val) )