weak-daemon

• About
• Installation
• Examples
  • Usage
  • Mocking
• Documentation

About

• Node.js object wrapper for unref'ed setInterval.
• weak means it will not prevent Node.js process to exit if event loop is empty.
• It will help you remember about routine context.
• No external dependencies.

Installation

Requires Node.js v4.8.7

$ npm install weak-daemon

Examples

• Ordinary function:

const WeakDaemon = require('weak-daemon').WeakDaemon
                                         
var daemon = new WeakDaemon(             
  102,                                   
  null,                                  
  () => { console.log('tick', 'tock') }  
);                                       
                                         
daemon.start(); // Will print 'tick' 'tock' every ~102 ms

..

/* (!) Note that multiple 'start' call without previous 'stop' will throw error */
daemon.start();     // First call made after ~102ms
daemon.start(false);// First call made after ~102ms
daemon.start(true); // First call made immediately;

..

daemon.start();
daemon.isRunning(); // true
daemon.stop();
daemon.isRunning(); // false
daemon.start();

• Equivalent of above example

var daemon = new WeakDaemon(
  102,
  null,
  console.log,
  ['tick', 'tock']
);

• Function that requires a caller context, because of this usage:

const worker = {
  data: {},
  updateData(source) {
    this.data = source.data;
  } 
}

var daemon = new WeakDaemon(
  102,
  worker,             /* So `this` will be handled properly on `updateData` call */
  worker.updateData,
  [data_source]
);

daemon.start();

• Example error scenario:

const worker = {
  data: {},
  source: {...},
  
  updateData() {
    this.data = this.source.data()
  }
}

var daemon = new WeakDaemon(
  101,
  null,               /* `this.source` will be undefined while daemon will call `updateData` */
  worker.updateData
);

/* Error - `this.source` is undefined */
daemon.start();

Mocking for test purposes:

/* your-lib.js */
const {getInstance} = require('weak-daemon');

// :(
const non_mockable_daemon = new WeakDaemon(...args);

// :)
const mockable_daemon = getInstance(...args);

/* test-your-lib.js */
const WD = require('weak-daemon');

WD.getInstance = () => { return your_mock; }

Alternative way:

/* your-lib.js */
const {WeakDaemon, getClass} = require('weak-daemon');

const non_mockable_daemon = new WeakDaemon(...args)

const MockableWeakDaemon = getClass();
const mockable_daemon = new MockableWeakDaemon(...args);

/* test-your-lib.js */
const WD = require('weak-daemon');

WD.getClass = () => { return YourMock; }

Documentation

class WeakDaemon

• constructor( interval_time, caller, task, task_args=[] )

  Arguments:

  • interval integer number - interval time of task call in milliseconds. Note this is not guarntee to call task every interval, it works exactly the same as setInterval(..).unref()
  • caller object | null - task's caller context (in case if task will use 'this' keyword)
  • task function - task that will be called every interval
  • [task_args] Array - list of arguments task will be called with.

• start( immediate_call )

  Start daemon.

  Arguments:

  • immediate_call - boolean, is task should be called immediately after start call. Default false.

• stop()

  Stop daemon (can be resterted by calling start).

• isRunning()

  Returns:

  • boolean, is daemon running

• interval getter for provided interval_time

• caller getter for provided caller

• task getter for provided task

• args getter for provided args ([] returned if not provided])

function getInstance

Provided for mocking purposes.

• Arguments: @see class WeakDaemon constructor

• Returns: instance of WeakDaemon.

function getClass

Provided for mocking purposes.

• Arguments: no

• Returns: WeakDaemon class.