Firebase: How to log the value returned from Firebase collection?

In my React Native app I get a value from Firebase using

this.getRef()
.doc(<something>)
.collection(<something>)
.doc(<something>)

I want to log the value returned by that, but I don’t know if it returns a promise. I’d like to do something like

let a = this.getRef()
  .doc(<something>)
  .collection(<something>)
  .doc(<something>)
console.log(a)

How should I approach this?