object.js

object.js provides a meta-constructor and a set of tools and utilities to aid in object/instance construction and implementing dynamic data and functionality inheritance within the established JavaScript prototypical object model and interfaces.

This is an alternative to the ES6 class syntax in JavaScript and provides several advantages:

• Simple way to define instance and "class" (constructor) methods, properties and attributes,
• Uniform and minimalistic definition syntax based on basic JavaScript object syntax, no special cases, special syntax or "the same but slightly different" ways to do things,
• Transparently based on JavaScript's prototypical inheritance model,
• Granular instance construction (a-la Python's .__new__(..) and .__init__(..) methods)
• Simple way to define callable instances (including a-la Python's .__call__(..))
• produces fully introspectable constructors/instances, i.e. no direct way to define "private" attributes or methods.
• Less restrictive:
  • new is optional
  • all input components are reusable
  • no artificial restrictions

Disadvantages compared to the class syntax:

• No syntactic sugar
• Slightly more complicated calling of parent (super) methods

Here is a basic comparison:

var L = object.Constructor('L', Array, {
    constructor_attr: 'constructor',

    method: function(){
        return 'constructor'
    },
}, {
    // prototype attribute (inherited)...
    attr: 'prototype',

    get prop(){
        return 42 },

    __init__: function(){
        this.instance_attr = 7
    },
})

class L extends Array {
    static constructor_attr = 'class'

    static method(){
        return 'class'
    }

    // instance attribute (copied)...
    attr = 'instance'

    get prop(){
        return 42 }

    constructor(){
        super(...arguments)	

        this.instance_attr = 7
    }
}

Contents

• object.js
  • Contents
  • Installation
  • Basic usage
    • Inheritance
    • Callable instances
  • Advanced usage
    • Low level constructor
    • Extending the constructor
    • Inheriting from native constructor objects
    • Extending native .constructor(..)
  • Components
  • Utilities
  • Limitations
    • Can not mix unrelated native types
  • License

Installation

$ npm install ig-object

Or just download and drop object.js into your code.

Basic usage

Include the code, this is compatible with both node's and RequireJS' require(..)

var object = require('ig-object')

Create a basic constructor...

// NOTE: new is optional here...
var A = new object.Constructor('A')

In JavaScript constructor B inherits from constructor A iff A.prototype is prototype of B.prototype. So to implement inheritance we simply need to link the prototypes of two constructors via .__proto__, Object.create(..) or other means.

var B = object.Constructor('B', A, {})

var C = object.Constructor('C', B, {})

Now we can test this...

var c = C() // or new C()

c instanceof C // -> true
c instanceof B // -> true
c instanceof A // -> true

Inheritance

//
//	  Base <--- Item
//
var Base = object.Constructor('Base', {
    proto_attr: 'prototype attr value',

    get prop(){
        return 'propery value' },

    method: function(){
        console.log('Base.method()') },

    // initializer...
    __init__: function(){
        this.instance_attr = 'instance'
    },
})

var Item = object.Constructor('Item', Base, {
    __init__: function(){
        // call the "super" method...
        object.parentCall(this.prototype.__init__, this)

        this.item_attr = 'instance attribute value'
    },
})

var SubItem = object.Constructor('SubItem', Item, {
    // ...
})

Callable instances

var Action = object.Constructor('Action',
    // constructor as a function...
    function(context, ...args){
        // return the instance...
        return this
    })

var action = new Action()

// the instance now is a function...
action()


// a different way to do the above...
//
// This is the same as the above but a bit more convenient as we do 
// not need to use Object.assign(..) or object.mixinFlat(..) to define
// attributes and props.

var Action2 = object.Constructor('Action2', {
    __call__: function(context, ...args){
        return this
    },
})

In the above cases both the function constructor and the .__call__(..) method receive a context argument in addition to this context, those represent the two contexts relevant to the callable instance:

• Internal context (this)
  This always references the instance being called
• External context (context) This is the object the instance is called from, i.e. the call context (window or global by default)

If the prototype is explicitly defined as a function then it is the user's responsibility to call .__call__(..) method.

Notes:

• the two approaches (function vs. .__call__(..)) will produce slightly different results, the difference is in .prototype, in the first case it is a function while in the second an object with a .__call__(..) method.
  (this may change in the future)

Advanced usage

Low level constructor

var LowLevel = object.Constructor('LowLevel', {
    __new__: function(context, ...args){
        return {}
    },
})

Like function constructor and .__call__(..) this also has two contexts, but the internal context is different -- as it is the job of .__new__(..) to create an instance, at time of call the instance does not exist and this references the .prototype object. The external context is the same as above.

Contexts:

• Internal context (this)
  References the .prototype of the constructor.
• External context (context) This is the object the instance is called from, i.e. the call context (window or global by default), the same as for function constructor and .__call__(..).

The value .__new__(..)returns is used as the instance and gets linked in the prototype chain.

This has priority over the callable protocols above, thus the user must take care of both the function constructor and prototype.__call__(..) handling.

Notes:

• .__new__(..) is an instance method, contrary to Python (the inspiration for this protocol). This is done intentionally as in JavaScript there is no distinction between an instance and a class and defining .__new__(..) in the class would both add complexity as well as restrict the use-cases for the constructor.

Extending the constructor

var C = object.Constructor('C',
    // this will get mixed into the constructor C...
    {
        constructor_attr: 123,

        constructorMethod: function(){
            // ...
        },

        // ...
    }, {
        instanceMethod: function(){
            // get constructor data...
            var x = this.constructor.constructor_attr

            // ...
        },
        // ...
    })

And the same thing while extending...

var D = object.Constructor('D', C,
    // this will get mixed into C(..)...
    {
        // ...
    }, {
        // ...
    })

Inheriting from native constructor objects

var myArray = object.Constructor('myArray', Array, {
    // ...
})

All special methods and protocols defined by object.js except for .__new__(..) will work here without change.

For details on .__new__(..) and native .constructor(..) interaction see: Extending native .constructor(..)

Extending native .constructor(..)

Extending .constructor(..) is not necessary in most cases as .__init__(..) will do everything generally needed, except for instance replacement.

var myArray = object.Constructor('myArray', Array, {
    __new__: function(context, ...args){
        var obj = Reflect.construct(myArray.__proto__, args, myArray)

        // ...

        return obj
    },
})

Components

Get sources for attribute

sources(<object>, <name>)
sources(<object>, <name>, <callback>)
    -> <list>

Get parent attribute value or method

parent(<prototype>, <name>)
    -> <parent-value>
    -> undefined

parent(<method>, <this>)
    -> <parent-method>
    -> undefined

Edge case: The parent(<method>, ..) has one potential pitfall -- in the rare case where a prototype chain contains two or more references to the same method under the same name, parent(..) can't distinguish between these references and will always return the second one.

Get parent property descriptor

parentProperty(<prototype>, <name>)
    -> <prop-descriptor>
    -> undefined

Get parent method and call it

parentCall(<prototype>, <name>, <this>)
    -> <result>
    -> undefined

parentCall(<method>, <this>)
    -> <result>
    -> undefined

Mixin objects into a prototype chain

mixin(<root>, <object>, ..)
    -> <object>

Mixin contents of objects into one

mixinFlat(<root>, <object>, ..)
    -> <object>

This is like Object.assign(..) but copies property objects rather than property values.

Make a raw (un-initialized) instance

makeRawInstance(<context>, <constructor>, ..)
    -> <object>

A shorthand to this is Constructor.__rawinstance__(context, ..).

Define an object constructor

Constructor(<name>)
Constructor(<name>, <prototype>)
Constructor(<name>, <parent-constructor>, <prototype>)
Constructor(<name>, <parent-constructor>, <constructor-mixin>, <prototype>)
Constructor(<name>, <constructor-mixin>, <prototype>)
    -> <constructor>

Shorthand to Constructor(..)

C(<name>, ..)
    -> <constructor>

Utilities

Align text to shortest leading whitespace

normalizeIndent(<text>)
normalizeIndent(<text>, <tab-size>)
    -> <text>

This is used to format .toString(..) return values for nested functions to make source printing in console more pleasant to read.

Limitations

Can not mix unrelated native types

At this point we can't mix native types, for example it is not possible to make a callable Array object...

This is not possible in current JavaScript implementations directly as most builtin objects rely on "hidden" mechanics and there is no way to combine or inherit them.

To illustrate:

// produces an Array that looks like a function but does not act like one...
var a = Reflect.construct(Array, [], Function)

// creates a function that looks like an array... 
var b = Reflect.construct(Function, [], Array)

So these will produce partially broken instances:

var A = object.Constructor('A', Array, function(){ .. })

var B = object.Constructor('B', Array, {
    __call__: function(){ .. },
})

Essentially this issue and the inability to implement it without emulation, shows the side-effects of two "features" in JavaScript:

• lack of multiple inheritance
• hidden protocols/functionality (namely: calls, attribute access)

Still, this is worth some thought.

License

BSD 3-Clause License

Copyright (c) 2019, Alex A. Naanou,
All rights reserved.