The Sorting Hat

The Sorting Hat sorts Firebase events into their Houses. It accomplishes this through what we shall call magic.

For muggles: This allows you to watch for new children added to a particular Firebase path and invoke a callback function.

var SortingHat = require('sortinghat'),
    hat = new SortingHat(new Firebase('https://example.firebaseio.com'));

hat.watch('/foo', function(snap) {
    console.log('new foo:', snap.val());
});

Methods

new SortingHat(firebase)

require('sortinghat') gives you this constructor. Pass in a ready-to-use Firebase object.

watch(path, [options,] [cb])

Watch path for new children. In order to not download all the data under this path, Sorting Hat requires you to use a well-defined ordering of data. You cannot watch for children added at arbitrary locations; they must be added to the end of the order.

• options.order
  • key - Items will be added with keys having a monotonically increasing alpha order. Suitable for use with push().
  • priority - Items will be added with a monotonically increasing priority.
  • anything else - Items will be objects containing this key, whose value will monotonically increase (ie a created timestamp).

trigger(path, [options,] [cb])

Watch path for new children. There are no constraints on order, however this requires that the Sorting Hat downloads all data from path.

When calling a Lambda function, the new child will be automatically deleted from Firebase after Lambda accepts the invocation.

WARNING! Only use trigger on a path where you plan on deleting the children shortly after they are created. In other words, path should usually be empty. If you ignore this advice, the Sorting Hat will use all your memory and/or crash.

responder(path, [options,] [cb])

Exactly like trigger -- watches path for new children with no constraints on order (and the associated caveats) -- except adds /request to the supplied path.

cb

The cb argument to watch, trigger, and responder can optionally take a callback function.

If you supply a function, it is invoked whenever there is a change. The one and only argument passed to the function is the Firebase Snapshot of the new child.

watch, trigger, and responder also return a FirebaseWatcher. This object is an EventEmitter that emits child_added events for watch and request events for trigger and responder.