title: return user.uid onAuthStateChanged
body: <p>I have small function and it works when I look in console: returns user.uid in console but I want to return uid to use in other function</p>
  
  <pre><code>newUserUid() {
  return firebase.auth().onAuthStateChanged(function(user) {
    if (user) {
     console.log(user.uid);
    }
  });
  }
  </code></pre>
  
  <p>I want to function return uid like this: <code>ewfwe3423sdfsdakmasd</code></p>