PubSub basics

Pubsub will only work after the user has logged in. You can check the connection by accessing skygear.pubsub.connected. Here, all the examples are using event ping.

Subscribing to an event

skygear.on('ping', (data) => {
  console.log(data);
});

Waiting for a single event

skygear.pubsub.once('event')
.then(_ => {
  // do stuff after event happened
});

or with ES7 async/await:

await skygear.pubsub.once('event');
// do stuff after event happened

Unsubscribing an event

Unsubscribing all handlers for an event

skygear.off('ping');

Unsubscribing a specific handler for an event

const handler = (data) => console.log(data);
skygear.on('ping', handler); // also returns handler

// later
skygear.off('ping', handler);

Check if an event has handler

skygear.pubsub.hasHandlers('ping');

Publishing an event

You can send a JavaScript object or native types (e.g. number, string, etc.) as data, and all the skygear users (including yourself) will receive this data with the correct type if they subscribed to event ping.

skygear.pubsub.publish('ping', data);

To publish a message to the channel through cloud code, please refer to the Cloud Functions Guide: Calling Skygear API - Pubsub Events.

Listening to Connection state

Skygear will automatically re-connect on connection drop. Skygear will also re-subscribe all existing handler on connection restore. So in normal case, you don't need to re-subscribe all your handler on re-connect.

We understand application may need to know the status of pubsub connection, we provide onOpen and onClose callback for that.

function welcome() {
  console.log('Chat are ready!');
  // Don't subscribe channel here, or yield to multiple function call on same
  // event
}

function warning() {
  console.log('Chat is temporarily unavailable');
}

const welcomeHandle = skygear.pubsub.onOpen(welcome);
const alertHandle = skygear.pubsub.onClose(warning);

// You may cancel the registered callback by calling cancel
welcomeHandle.cancel();
alertHandle.cancel();