How to read keys of childs of a reference in firebase realtime database?

Question

I have a reference to "a" named as 'ref'. And I want to read all the key(name,age and car) of the child of the reference. If my JSON looks like ths:

{"a":{ "name":"John", "age":30, "car":null } }

Answer 1

The following should do the trick:

  firebase
    .database()
    .ref('a')
    .once('value')
    .then(function (snapshot) {
      var valObj = snapshot.val();
      for (var key in valObj) {
        var value = valObj[key];
        console.log(key + ': ' + value);
      }
    });

As explained in the doc:

Any time you read data from the Database, you receive the data as a DataSnapshot. A DataSnapshot is passed to the event callbacks you attach with on() or once(). You can extract the contents of the snapshot as a JavaScript object by calling the val() method.

We use one of the techniques described here to loop over all the properties of the object.

---

If you know the names of the properties you want to get, you can do, for example:

  firebase
    .database()
    .ref('a')
    .once('value')
    .then(function (snapshot) {
      var valObj = snapshot.val();
      console.log(valObj.name);
      console.log(valObj.car);
    });

Answer 2

  firebase
    .database()
    .ref('a').on("child_added", snap => {
 });