@textile/hub > Client > listen

Client.listen() method

listen opens a long-lived connection with a remote node, running the given callback on each new update to the given instance. The return value is a close function, which cleanly closes the connection with the remote node.

Signature:

listen<T = any>(threadID: ThreadID, filters: Filter[], callback: (reply?: Update<T>, err?: Error) => void): grpc.Request;

Parameters

Parameter	Type	Description
threadID	ThreadID	the ID of the database
filters	Filter[]	contains an array of Filters
callback	(reply?: Update<T>, err?: Error) => void	The callback to call on each update to the given instance.

Returns:

grpc.Request

Example 1

import {Client, ThreadID, Update} from '@textile/hub'

interface Astronaut {
  name: string
  missions: number
  _id: string
}
function setupListener (client: Client, threadID: ThreadID) {
  const callback = (update?: Update<Astronaut>) => {
    // Not safe if more than the Astronauts collection existed in the same DB
    if (!update || !update.instance) return
    console.log('New update:', update.instance.name, update.instance.missions)
  }
  const closer = client.listen(threadID, [], callback)
  return closer
}

Example 2

Listen to only CREATE events on a specific Collection.

import {Client, ThreadID, Update} from '@textile/hub'

interface Astronaut {
  name: string
  missions: number
  _id: string
}
function setupListener (client: Client, threadID: ThreadID) {
  const callback = (update?: Update<Astronaut>) => {
    if (!update || !update.instance) return
    console.log('New update:', update.instance.name, update.instance.missions)
  }
  const filters = [
    {collectionName: 'Astronauts'},
    {actionTypes: ['CREATE']}
  ]
  const closer = client.listen(threadID, filters, callback)
  return closer
}