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Objects with managed lifecycles for Node and the browser.


  • Async creation: Function calls are automatically deferred until constructor invokes callback
  • All function calls are observable and can be intercepted
  • Create hierarchies of instances that get destroyed together

How does it work?

Licy types can be defined in two ways. Using an object:

var Hello = licy.define({
  constructor: function (name) { = name;
  log: function () {
    console.log('Hello ' +;

Or using a function:

var Hello = licy.define(function (name) {
  return {
    log: function () {
      console.log('Hello ' + name);

Types that where defined with licy can be newed up like any other JavaScript type. Both of the examples above can be used like this:

var hello = new Hello('world');
hello.log(); // logs "Hello world" 

Async object creation

Any defined type can be changed to be created asynchronously:

var Hello = licy.define(function (name, callback) {
  setTimeout(callback, 500);
  return { /* as above */ };
var hello = new Hello('world');
hello.log(); // logs "Hello world" after 500 milliseconds 

All function calls will be implicitly deferred until the constructor invoked the callback.

As a consequence, obtaining the return value of a function only works with callbacks:

var Hello = licy.define(function (name) {
  return {
    get: function () {
      return 'Hello ' + name;
var hello = new Hello('world');
console.log(hello.get()); // logs "Hello undefined" 
hello.get(function (err, value) {
  console.log(value); // logs "Hello world" 

Note that the callback follows the Node.js (err, value) convention.

Observing and intercepting calls

Each licy instance inherits the hub.js event emitter API and emits an event for each function call:

hello.on('log', function () {
  // Invoked on hello.log() calls 

Filters can be used to intercept calls:

hello.addFilter('log', function (next) {
  // Defer all calls by 500 milliseconds: 
  setTimeout(function () {
  }, 500);

Destroying instances

Each licy instance has a destroy([callback]) implementation which emits a "destroy" event and invokes the defined destroy function, if given:

var Hello = licy.define(function (name) {
  return {
    destroy: function () {
      console.log('Bye ' + name);
var hello = new Hello('world');

Calling licy.destroy() will destroy all existing licy instances. This can be used to shut down an application cleanly, e.g. closing a server gracefully.

To bind the lifecycle of one object to another, invoke a.destroyWith(b). Use create(definition) to bind a child object to a parent: var b = a.create(B).

Install with npm

npm install licy --save

Browser support

Use Browserify to create a standalone file. The licy test suite passes on IE 9, 10, 11, Chrome *, Filefox * and PhantomJS.


Licy is a hub.js instance with these additions:

  • Licy: The Licy constructor (licy instanceof licy.Licy is true)
  • define([definition]): Defines a new type. The definition must be either ommitted, of type function or an object:
    • No definition: A plain licy type is returned that creates objects with the same API as the parent object.
    • function: The function is used as the constructor and is expected to return the API as an object.
    • object: Defines the API directly. A constructor can be defined optionally. The returned type creates new Licy instances. Each instance is derived from Licy itself and also inherits the hub.js API. All created instances are destroyed when the defining instance is destroyed.
  • create([definition]): Creates an instance that will be destroyed with this instance. If definition is not a type, define(definition) is called before creating an instance.
  • destroy([callback]): Emits the destroy event on the licy instance and all children. If a callback is given, it is invoked after this instance and all children are destroyed. If an error occurred, it is passed as the only argument to the callback.
  • destroyWith(type): Destroy this instance when type is destroyed.
  • extend(Super, definition): Defines a new type which is derived from the Super type. Instances of the new type are instanceof Super. If a constructor is given, or if definition is a function, the super constructor must be explicitly invoked with If a method is defined that already exists in the super type, it is registered as a filter.

Type API

Each type returned by licy.define() is a Licy instance with these additions:

  • Type.extend(definition): Is a shortcut for licy.extend(Type, definition).


Each type instance and the root licy object emit these events:

  • define(type, callback): When a new child type is defined.
  • create(instance, type, callback): When a child instance is created.
  • destroy(callback): When the instance is destroyed.

The prototype of custom defined types is a licy instance itself. It can be used to emit and subscribe global type specific events. These events are always emitted:

  • instance.create(instance, type, callback): When a new instance is created.
  • instance.destroy(instance, error, callback): When an instance is destroyed. If an error occurred during destruction, the Error is passed on as error.


  • npm install to install the dev dependencies
  • npm test to lint, run tests on Node and PhantomJS and check code coverage