nextOrObserver:Object type definition in typescript doesn't allow type inference

[esprehn]

[REQUIRED] Describe your environment

• Operating System version: OS X
• Firebase SDK version: 3.6.8
• Firebase Product: all (noticeable in auth)

[REQUIRED] Describe the problem

The firebase.d.ts file contains the following type definitions:

onAuthStateChanged (nextOrObserver : Object , error ? : (a : firebase.auth.Error ) => any , completed ? : ( ) => any ) : ( ) => any ;

but this means you can't just pass a function like

.onAuthStateChanged((user) => {
 ...
});

and let |user| by in inferred type, because typescript thinks this method takes an Object. If we look at closure externs they're more specific:

firebase-js-sdk/externs/firebase-auth-externs.js

Line 873 in bc94aae

* @param {!Object|function(?firebase.User)}

@param {!Object|function(?firebase.User)}

which would let you pass a callback without explicitly naming the type.

Steps to reproduce:

in typescript write:

firebase.auth().onAuthStateChanged((user) => {
  console.log(user);
});

In general the "Observer" concept is mentioned in the API type definitions and docs, but I don't see anything documented about what an Observer object would be. Everything just passes a function here, is that some Firebase internal type?

Ideally the type definitions here would be specific enough that typescript could infer the argument types of all of the callbacks used in all the various firebase apis. :)

[google-oss-bot]

Hey there! I couldn't figure out what this issue is about, so I've labeled it for a human to triage. Hang tight.

[jsayol]

@esprehn - an observer in this case would be an object with any of the next, error, and complete methods.

You're right, though. The typings should be fixed.

[jshcrowthe]

This was fixed in #56, thanks @esprehn and @jsayol!