Storyboard Listener API

For an example of how to implement a Storyboard listener (plugin), check out the ConsoleListener, arguably the simplest built-in listener. Listeners should follow the API described in this document.

Listener methods

constructor() (optional)

• config object: user configuration options. Should typically be merged with some defaults and stored in the listener instance.
• context object:

  • hub object: the hub instance this listener is attached to. See Hub API for listeners below.

  • chalk object: a pre-configured, always-enabled version of the chalk library.

  • mainStory object: Storyboard's main story, which can be used to generate logs the same way as a library user:

    class MyListener {
      constructor(config, { hub, mainStory }) {
        this.hub = hub;
        this.mainStory = mainStory;
      }
    
      init() {
        this.mainStory.info('myListener', 'Listener is up and running!');
      }
    }
    

getConfig() (mandatory)

• No arguments
• Returns object: current listener configuration.

configure(config) (optional)

• Merges the provided object with the current configuration. You may want to support changes to configuration after initialisation, but this is not mandatory.
• config object: new configuration options.
• No return value

init() (optional)

• Executes initialisation operations, e.g. connects to a database, opens a file, etc.
• No arguments
• No return value

tearDown() (optional)

• Executes tear-down operations, e.g. disconnects from a database, closes a file, etc.
• No arguments
• No return value

process() (mandatory)

• Processes a message from the hub, e.g. saves records to a database, writes them to a file, relays them to a browser extension, uploads them to a server, etc.
• msg object: a message from the hub, containing:
  • type string: the type of message, e.g. RECORDS, LOGIN_REQUEST, LOGIN_RESPONSE, SET_SERVER_FILTER... Typical listeners discard messages with type other than RECORDS.
  • hubId string: the ID of the hub to which the originating listener is attached. Typical listeners discard messages from hubs other than the one they are attached to.
  • src string: an indication of the message originator, e.g. STORIES (a story), WS_CLIENT (the WebSocket Client listener; used for signalling). When a message is relayed by a listener, it should not change its src field.
  • data any: the message payload; its format is defined by the message type: e.g. an array of log records for RECORDS, a filter string for SET_SERVER_FILTER, clock sync data for CLOCKSY, etc.
• No return value

Listener module

Wrap your listener in a module and export a creator function:

import { addDefaults } from 'timm';
const DEFAULT_CONFIG = { /* ... */ };
const create = (userConfig, context) =>
  new MyListener(addDefaults(userConfig, DEFAULT_CONFIG), context);

export default create;

Users can add your listener in the standard way:

import myListener from './myListener';
import { addListener } from 'storyboard';
addListener(myListener, { /* custom config */ });

Hub API for listeners

The listener constructor is passed a reference to some hub methods:

hub.getHubId()

• Provides the ID of the hub our listener is attached to.
• No arguments
• Returns string: hub ID

hub.emitMsg()

• Re-broadcasts a message (that has been previously received via a call to processMsg()).
• msg object: the message to be relayed (contents are described in processMsg() above)
• srcListener object: pass this if you don't want to get the message back from the hub when it re-broadcasts it.
• No return value

hub.emitMsgWithFields()

• Builds a new message a broadcasts it to all attached listeners.
• src string: an identifier for the originating listener, e.g. WS_CLIENT.
• type string: see msg contents in processMsg() above.
• data any: see msg contents in processMsg() above.
• srcListener object: pass this if you don't want to get the message back from the hub when it broadcasts it.