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Moog provides object oriented programming services, with rich support for asynchronous constructors, modification of constructor parameters by subclasses, and "implicit subclassing" that allows a class to be replaced in a way that is transparent to end users.

Moog implements the "self pattern," so you never have to worry about using .call, .apply or .bind.

moog synthesizes objects with full support for inheritance. You can define them with any combination of synchronous and asynchronous constructors, specify default options easily, and modify options before they are seen by base classes.

const moog = require('moog')();

moog.define('baseclass', {
  color: 'blue',
  // sync constructor
  construct: function(self, options) {
    self._options = options;

    self.jump = function(howHigh) {
      return 'I jumped ' + howHigh + ' pixels high';

moog.define('subclass', {
  color: 'red',
  // async constructor
  construct: async function(self, options) {
    self.candy = await goGetTheCandy();

const obj = await moog.create('subclass', { age: 20 });
assert(obj._options.color === 'red');
assert(obj.jump(5) === 'I jumped 5 pixels high');

Factory function

To create an instance of moog:

var moog = require('moog')();

You may also pass options:

var moog = require('moog')({
  defaultBaseClass: 'superclass'

moog.define(className, definition)

Defines a new class. className is a string.

moog.define('baseclass', {
  // Set the default value of an option
  color: 'red',
  // Simple synchronous constructor
  construct: function(self, options) {
    self._options = options;

The definition object can contain the properties construct, beforeConstruct, and afterConstruct, which are functions invoked by moog.create, as described below. The extend property allows for subclassing. All other properties are treated as defaults for the options object provided when constructing an instance of the class.

To subclass another class, just extend it by name in the definition of your subclass:

moog.define('subclass', {
  // Change the default value of an option
  color: 'blue',
  extend: 'baseclass'

Default base class

If you set the defaultBaseClass option of moog and do not explicitly extend anything for a particular class, then that class will extend the defaultBaseClass. If you wish to override this behavior for a specific class, just set extend to false.

Implicit subclassing

If you define the same class twice without setting extend the second time, an implicit subclass is created.

The new version subclasses the old one, effectively "patching" it with new options and behavior without having to redefine everything. All other types that subclass that name now subclass the new version.

The property of each instance will have a my- prefix (or more than one, if such implicit subclassing is repeated).

Fallback base classes

If you are not sure if there is an existing definition for a class, you can use extendIfFirst to specify a fallback base class. This is helpful when encouraging third-party developers to optionally define a type themselves.

Defining many types at once

For convenience, you may pass an object containing properties that define many different types:

  // This is equivalent to calling moog.define for each of these types
  'baseclass': {
    // See above for example of a definition
  'subclass': {
    // See above for example of a definition

moog.redefine(className, definition)

Explicitly replaces any previous definition of className with a new one. Does not subclass the old class. If there was no old definition, this method is equivalent to moog.define.

moog.isDefined(className, options)

Returns true if the class is defined, whether explicitly or via the autoloader option. That is, moog.create will succeed for className, provided that the constructor does not signal an error. If the class is available via the autoloader, this method returns true but does not leave the definition in place.

The options argument may be omitted entirely. If options.autoload is explicitly set to false, no attempt to test for the ability to load the class via the autoloader is made.

await moog.create(className, options)

moog.createSync(className, options)

Creates an object of the specified class, passing options to override any default options set in moog.define.

moog.define('myObject', {
  color: 'blue',
  construct: function(self, options) {
    self.color = options.color;

var myObject = moog.create('myObject', { color: 'purple' });
alert("My object is " + myObject.color); // "My object is purple"

When create is called, moog will first call beforeConstruct, starting with the deepest subclass first. Then the construct methods are called, if present, starting with the base class and ending with the final subclass. Finally the afterConstruct methods are called, if present, starting with the base class and ending with the final subclass.

moog.create is asynchronous, and so it must be awaited. You can also create an object with moog.createSync, which does not require await. However, createSync will throw an exception if any of beforeConstruct, construct or afterConstruct throw a promise, including those in parent classes, etc.

// Always works
const object = await moog.create('myObject', { color: 'purple' });

// Throws an exception if any construction-related functions return
// a promise
const object = moog.createSync('myObject', { color: 'purple' });

The __meta property

obj will always have a __meta property, which contains an array of metadata objects describing each module in the inheritance chain, starting with the base class. The metadata objects will always have a name property. moog-require also provides dirname and filename. This is useful to implement template overrides, or push browser-side javascript and styles defined by each level.

my- utilities

The methods isMy, myToOriginal, and originalToMy can be used to manipulate class names, detecting, adding or removing a my- prefix as appropriate while accommodating npm namespaces in class names. If the class name contains an npm package name (such as @namespace/foo), the prefix is applied to the second part, for example @namespace/my-foo.


2.1.2 (2020-08-12): Updates ESLint to address dependency warnings.

2.1.1: actually use the originalToMy utility when implicitly subclassing.

2.1.0: utilities to manipulate the my- prefix safely for type names with and without an npm namespace.

2.0.1: npm update, plus removal of package-lock.json which is not appropriate in libraries. No code changes.

2.0.0: this is a major version change with significant, intentional bc breaks.

  • beforeConstruct, construct and afterConstruct may all be async functions. They can also be simple synchronous functions of course.
  • Support for callbacks has been removed.
  • beforeConstruct, construct and afterConstruct all receive the same arguments: (self, options).
  • The mirror method has been removed as we do not intend to use it in Apostrophe 3.x.
  • The createAll method has been removed as it has seen little use.
  • Explicit browser support has been removed, you may use 2.0 in the browser via webpack, browserify, etc. with appropriate Babel presets to allow async/await in your browser of choice.

1.0.3: nudging past npm not making 1.0.2 available for some reason; no code changes.

1.0.2: in addition to the shallow top-level clone, we must also clone the __meta property and its __meta.chain subproperty to ensure they are not reused between instances of moog. No other properties of the definition are objects subject to modification.

1.0.1: shallowly clone each definition to avoid numerous problems when multiple instances of moog intended to be separate worlds wind up sharing the same definition objects due to the require cache. A shallow clone gives us independent __meta properties, which are all we need to solve the problem. Definitions are few, instances are many and the clone is shallow, so this is not a significant performance hit.

Also, use the apostrophe eslint test configuration. This required various syntax updates and flushed out a few oddities although no bugs.

1.0.0: updated lodash and mocha to satisfy npm audit. Code is still compatible with lodash 3.x as well, for those using the @sailshq/lodash fork for bc, and for Apostrophe's frontend which uses that version and shouldn't push multiple versions.

0.3.1: new instanceOf method. Given an object and a type name, this method returns true if the object is of the given type or a type that extends it.

0.3.0: new options argument to isDefined, which may contain an autoloader: false property to prevent isDefined from attempting to test whether the type can be defined by the autoloader.

0.2.4: throw the proper exception when synchronously creating a type that extends an undefined type. (Previously an exception was thrown, but it wasn't informative. It was an accidental benefit of trying to invoke a nonexistent callback.)

0.2.3: exceptions thrown for attempts to synchronously create types with asynchronous beforeConstruct/construct/afterConstruct methods now include the correct name of the type or ancestor type that requires the call to be asynchronous.

0.2.2: if afterConstruct expects a callback, calling create synchronously should throw an error. This is a bug fix, so no minor version bump is required.

0.2.1: __meta property is available in beforeConstruct. I regard this as a bug fix as the idea was always to have this information be available as early as possible.

0.2.0: added support for mirror, which allows browser-side type hierarchies to match those used on the server side. To add actual code for those types, take advantage of the implicit subclassing feature of moog.define.

0.1.5: added support for extendIfFirst, useful when you don't know if there is an existing definition of the type. report certain errors synchronously when creating objects synchronously.

0.1.4: allow setting extend to false to explicitly turn off defaultBaseClass for a particular type. Also corrected the unit test for defaultBaseClass (the feature worked, but the test was wrong).

0.1.3: never pass options to afterConstruct. We formerly were correctly leaving it off in the async case, but passing it in the sync case.

0.1.2: Updated some documentation.

0.1.1: added afterConstruct, another optional method which is invoked after construct. Like beforeConstruct and construct it can be sync or async. Unlike those methods it DOES NOT take the options parameter.

0.1.0: bc break: __meta is now an object with chain and name properties. chain is the array of subclass metadata objects as before. name is the class name being instantiated. Also, __meta is fully populated before any constructors are called.


Moog provides powerful module subclassing.


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