on()

on(type, filter, callback): RealtimeChannel

Listen for channel events. Bind presence and postgres_changes before subscribe().

Parameters

type

"broadcast" | "presence" | "postgres_changes" | "system"

Event type

filter

object

Filter, such as { event } or a Postgres CDC filter

callback

(payload) => void

Event callback

Response

RealtimeChannel

RealtimeChannel

Current channel, for chaining

Example

Broadcast

channel.on("broadcast", { event: "cursor-pos" }, (payload) => {
  console.log(payload.event, payload.payload);
});

Presence

channel
  .on("presence", { event: "sync" }, () => {
    console.log(channel.presenceState());
  })
  .on("presence", { event: "join" }, ({ newPresences }) => {
    console.log(newPresences);
  })
  .on("presence", { event: "leave" }, ({ leftPresences }) => {
    console.log(leftPresences);
  });

Postgres CDC

channel.on(
  "postgres_changes",
  { event: "*", schema: "public", table: "messages" },
  (payload) => {
    console.log(payload.eventType, payload.new, payload.old);
  }
);