Interface OnDisconnect

If a write has been queued for this location via a set() or update() at a parent location, the write at this location will be canceled, though all other siblings will still be written.

example

var ref = admin.database().ref("onlineState");
ref.onDisconnect().set(false);
// ... sometime later
ref.onDisconnect().cancel();

set() is especially useful for implementing "presence" systems, where a value should be changed or cleared when a user disconnects so that they appear "offline" to other users. See Enabling Offline Capabilities in JavaScript for more information.

Note that onDisconnect operations are only triggered once. If you want an operation to occur each time a disconnect occurs, you'll need to re-establish the onDisconnect operations each time.

example

var ref = admin.database().ref("users/ada/status");
ref.onDisconnect().set("I disconnected!");

The values argument contains multiple property-value pairs that will be written to the Database together. Each child property can either be a simple property (for example, "name") or a relative path (for example, "name/first") from the current location to the data to update.

As opposed to the set() method, update() can be use to selectively update only the referenced properties at the current location (instead of replacing all the child properties at the current location).

See https://firebase.google.com/docs/reference/admin/node/admin.database.Reference#update for examples of using the connected version of update.

example

var ref = admin.database().ref("users/ada");
ref.update({
   onlineState: true,
   status: "I'm online."
});
ref.onDisconnect().update({
  onlineState: false,
  status: "I'm offline."
});