Collar.js Addon

You can extend collar with addon. Now it supports two extension points:

observers
operators

An addon is simply a javascript object with two extension point fields:

module.exports = {
  observers: {
    // key: observer pairs
  },
  operators: {
    // key: operator pairs
  }
}

Usage

const collar = require('collar.js');
collar.use(myAddon);

Operator

Operator is a function, which returns a node instance.

An example throttle operator

// first create a node class
class Throttle extends Node {
  constructor(options, eventemitter) {
    super(options, eventemitter);
    this._type = "throttle";
    this.ms = options.ms;
    this.last = new Date().getTime();
  }
  onSignal(signal) {
    let now = new Date().getTime();
    if (now - this.ms >= this.last) {
      this.last = now;
      this.send(signal);
    }
  }
}

// next, create operator by initiating the node in a function with arguments
function throttle(ms) {
  return new Throttle({
    ms,
  });
}

// export the addon by putting the operator in operators object
const myAddon = {
  operators: {
    throttle
  }
}

// register it
const collar = require('collar.js');
collar.use(myAddon);

const ns = collar.ns('com.collartechs.test');

// the registered operator accepts the exact number of arguments defined in your operator function
const throttleNode = ns.throttle(100);

Observer

Observer is used to monitoring the signal and node when node is processing signals. An observer is a function:

function observer(when, node, ...) {}

when: string, the monitoring phase, one of 'send', 'onReceive', 'to'
node: Node, which node is currently monitoring

According to different monitoring phase, there could be additional arguments. See below:

when node received a signal

function observer(when, node, signal) {}

when === 'onReceive'
node: the current node
signal: the signal to received

when node sends a signal

function observer(when, node, signal) {}

when === 'send'
node: the current node
signal: the signal to be sent

when node connects to another node

function observer(when, node, downstreamNode) {}

when === 'send'
node: the current node
downstreamNode: the node to connect to

Example:

A logger to log all signals send by nodes

module.exports = {
  observers: {
    logger: function(when, node, signal) {
      if (when !== 'send') return;
      console.log(node.id, 'send', signal.payload);
    }
  }
}

Addon