object.js/README.md

# object.js

_object.js_ is a set of tools and abstractions to create and manage 
constructors, objects and prototype chains in idiomatic JavaScript.

This is an alternative to the ES6 `class` syntax in JavaScript and provides 
several advantages:  
- _Uniform and minimalistic_ definition "syntax" based on basic JavaScript 
  object literals. No special cases, special syntax or _"the same but slightly
  different"_ ways to do things, trying to adhere to 
  [POLS](https://en.wikipedia.org/wiki/Principle_of_least_astonishment)
  as much as possible,
- _Transparently_ based on JavaScript's prototypical inheritance model,
- Produces fully introspectable constructors/instances,
- Does not try to emulate constructs foreign to JavaScript (i.e. classes),
- Granular 2-stage instance construction and initialization (a-la 
  _Python's_ `.__new__(..)` and `.__init__(..)` methods),
- Simple way to define callable instances (including a-la _Python's_ 
  `.__call__(..)`),
- Less restrictive:
	- `new` is optional,
	- all input components are reusable JavaScript objects,
	- no artificial restrictions.

Disadvantages compared to the `class` syntax:  
- No _syntactic sugar_,
- Slightly more complicated calling of `parent` (_super_) methods.

Note that the produced constructors and objects are functionally 
identical (almost) to the ones produced via ES6 classes and are 
interchangeable with them.


Here is a basic comparison:
<table border="0" width="100%">
<tr valign="top">
<td width="50%">

_object.js_
```javascript
var A = object.Constructor('A', {
	// prototype attribute (inherited)...
	attr: 'prototype',

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

var B = object.Constructor('B', A, {
	constructor_attr: 'constructor',

	constructor_method: function(){
		return 'constructor'
	},
}, {
	get prop(){
		return 42 },

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

- No _direct_ way to do "private" definitions,
- Clear separation of constructor and `.prototype`  
  For example, in `B`:
	- First block (optional) is merged with `B`,
	- Second block _is_ the `B.prototype`,
- No special syntax, stands out less.

</td>
<td>

_ES6_
```javascript
class A {
	// instance attribute (copied)...
	attr = 'instance'

	method(){
		// ...
	}
}

class B extends A {
	static constructor_attr = 'class'

	static constructor_method(){
		return 'class'
	}

	get prop(){
		return 42 }

	constructor(){
		super(...arguments)	

		this.instance_attr = 7
	}
}
```
- Syntax pretty but _misleading_;  
  calling a _constructor_ a class is not correct,
- `static` and instance definitions are not separated,
- lots of details done non-transparently under the hood.

</td>
</tr>
</table>



## Contents
- [object.js](#objectjs)
	- [Contents](#contents)
	- [Installation](#installation)
	- [Basic usage](#basic-usage)
		- [Inheritance](#inheritance)
		- [Callable instances](#callable-instances)
		- [Mix-ins](#mix-ins)
	- [Advanced usage](#advanced-usage)
		- [Low level constructor](#low-level-constructor)
		- [Extending the constructor](#extending-the-constructor)
		- [Inheriting from native constructor objects](#inheriting-from-native-constructor-objects)
		- [Extending native `.constructor(..)`](#extending-native-constructor)
	- [Components](#components)
		- [`STOP`](#stop)
		- [`sources(..)`](#sources)
		- [`values(..)`](#values)
		- [`parent(..)`](#parent)
		- [`parentProperty(..)`](#parentproperty)
		- [`parentCall(..)`](#parentcall)
		- [`mixin(..)`](#mixin)
		- [`mixins(..)`](#mixins)
		- [`hasMixin(..)`](#hasmixin)
		- [`mixout(..)`](#mixout)
		- [`mixinFlat(..)`](#mixinflat)
		- [`RawInstance(..)`](#rawinstance)
		- [`Constructor(..)` / `C(..)`](#constructor--c)
	- [Utilities](#utilities)
		- [`normalizeIndent(..)` / `normalizeTextIndent(..)`](#normalizeindent--normalizetextindent)
		- [`match(..)`](#match)
	- [Limitations](#limitations)
		- [Can not mix unrelated native types](#can-not-mix-unrelated-native-types)
	- [License](#license)


## Installation

```shell
$ npm install ig-object
```

Or just download and drop [object.js](object.js) into your code.



## Basic usage

Include the code, this is compatible with both [node's](https://nodejs.org/) and
[RequireJS'](https://requirejs.org/) `require(..)`
```javascript
var object = require('ig-object')
```

Create a basic constructor...

```javascript
// NOTE: new is optional here...
var A = new object.Constructor('A', {})

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

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

Now we can test this...
```javascript
var c = C() // or new C()

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

**Note:**
- in `object.Constructor('X', A)` the second argument is used as the 
  _prototype_, to use `A` as a parent constructor add an empty object 
  as a third argument, i.e. 'object.Constructor('X', A, {})'  
  (see: [`Constructor(..)` / `C(..)`](#constructor--c) for more info)


### Inheritance
```javascript
//
//	  Base <--- Item <--- SubItem
//
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, {
	method: function(){
		// ... 

		// call the "super" method...
		return object.parentCall(Item.prototype, 'method', this, ...arguments)
	},

	__init__: function(){
		// call the "super" method...
		object.parentCall(this.__init__, this, ...arguments)

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

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


### Callable instances

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

// a more flexible approach...
//
// 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){
		// call the callable parent...
		return object.parentCall(Action2.prototype, '__call__', this, ...arguments)
	},
})


var action = Action()
var action2 = new Action2()

// the instances are now functions...
action()
action2()
```

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.

When calling the parent passing `'__call__'` will get the parent in both 
the function and `.__call__(..)` implementations, but extra care must be 
taken in passing the reference prototype to `.parentCall(..)`, the instance
is implemented as a proxy function that will pass the arguments to the 
implementation (i.e. `this.constructor.prototype(..)`) so this proxy 
function as well as the `.constructor.prototype(..)` are valid implementations
and both will be retrieved by `sources(this, '__call__')`, 
`values(this, '__call__')` and by extension `parent(this, '__call__')` 
and friends, so this is another reason not to use `this` in the general 
case.


**Notes:**
- The two approaches (_function_ vs. `.__call__(..)`) will produce 
  functionally identical but structurally different constructors/objects, 
  the difference is in `.prototype` -- what is defined as the prototype
  _is_ the prototype (_POLS_), so we get:

  	- _prototype function_ -> `.prototype` is that exact function object,
	- `.__call__(..)` -> `.prototype` is _the_ object with the `.__call__(..)` 
	  method.

  The instance in both cases is a function wrapper that will proxy the 
  call to the corresponding implementation.
  (this may change in the future)
- Making an object callable does not guarantee that `<obj> instanceof Function`
  will be `true`, though `typeof(<obj>) == 'function'`will always work.
  To satisfy the `instanceof Function` test the prototype tree must be 
  rooted in `Function`.


### Mix-ins

Prototype-based mixin...
```javascript
var utilityMixin = {
	utility: function(){
		// ...
	},
}

var Base = object.Constructor('Base') 

// normal instance prototype chain:
//	b -> Base.prototype -> .. 
//
var b = Base()

// mixin directly into the instance...
//
// now the prototype chain looks like this:
//	b -> mixinFlat({}, utilityMixin) -> Base.prototype -> ..
//
object.mixin(b, utilityMixin)
```

`.mixin(..)` will copy the contents of `utilityMixin` into the prototype 
chain between `b` and `b.__proto__`.

We can also remove the mixin...
```javascript
o.mixout(b, utilityMixin)
```

The mixed-in data is removed iff a [matching](#match) object is found in 
the chain with the same attributes as `utilityMixin` and with each 
attribute matching identity with the corresponding attribute in the mixin.


Constructor-based mixin...
```javascript
var UtilityMixin = function(parent){
	return object.Constructor(parent.name + '+utils', parent, utilityMixin) }

var Mixed = object.Constructor('Mixed', UtilityMixin(Base), {
	// ...
})

var m = Mixed()
```


## Advanced usage

### Low level constructor

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

```

Like [_function constructor_ and `.__call__(..)`](#callable-instances) 
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.


### Extending the constructor

```javascript
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...
```javascript
var D = object.Constructor('D', C, {
	// ...
}, {
	// ...
})
```


### Inheriting from native constructor objects

```javascript
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 native `.constructor(..)`

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

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

		// ...

		return obj
	},
})
```



## Components

Note that all of the following are generic and will work on any relevant
JavaScript object.

For example, this will happily create a normal native array object 
`['a', 'b', 'c']`:
```javascript
var l = object.RawInstance(null, Array, 'a', 'b', 'c')
```



### `STOP`

Used in [`sources(..)`](#sources), [`values(..)`](#values) and 
[`mixins(..)`](#mixins) to stop the search before it reaches the top of 
the prototype chain.


### `sources(..)`

Get sources for attribute
```
sources(<object>, <name>)
sources(<object>, <name>, <callback>)
	-> <list>
```

```
callback(<source>)
	-> STOP 
	-> undefined
	-> <value>
```

The `callback(..)` controls the output of `sources(..)` by returning 
one of the following:

- `object.STOP`  
  This will make `sources(..)` stop and return the `<list>` up to and 
  including the object that triggered the _stop_.
- `undefined`  
  Add the object triggering `callback(..)` in `<list>` as-is and continue. 
- array  
  The containing values will be merged into the result list and continue.
  This is a way to either skip an object by returning `[]` or multiple 
  values instead of one.
- `<value>`  
  Add to the resulting `<list>` as-is instead of the object triggering 
  `callback(..)` and continue.


Special case: get callable implementations
```
sources(<object>, '__call__', ..)
	-> <list>
```

This will get the callable implementations regardless of the actual
implementation details, i.e. both function prototype or `.__call__(..)` 
methods will be matched.


### `values(..)`

Get values for attribute in prototype chain
```
values(<object>, <name>)
values(<object>, <name>, <callback>)
	-> <list>
```

```
callback(<value>, <source>)
	-> STOP 
	-> undefined
	-> <value>
```


Get property descriptors for attribute in prototype chain
```
values(<object>, <name>, true)
values(<object>, <name>, <callback>, true)
	-> <list>
```

```
callback(<descriptor>, <source>)
	-> STOP 
	-> undefined
	-> <value>
```


Special case: get callable implementations
```
values(<object>, '__call__', ..)
	-> <list>
```

This will return the callable objects themselves or the value of `.__call__`.



See [`sources(..)`](#sources) for docs on `callback(..)` and special cases.

### `parent(..)`

Get parent attribute value or method
```
parent(<prototype>, <name>)
	-> <parent-value>
	-> undefined
```

It is recommended to use the relative`<constructor>.prototype` as 
`<prototype>` and in turn not recommended to use `this` or `this.__proto__` 
as they will not provide the appropriate reference point in the prototype 
chain for the current method and may result in infinite recursion.

For access to parent methods the following special case is better.

```
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._


Special case: get the parent callable implementation
```
parent(<prototype>, '__call__')
	-> <parent-value>
	-> undefined
```

See [`sources(..)`](#sources) for more info on the special case.


### `parentProperty(..)`

Get parent property descriptor
```
parentProperty(<prototype>, <name>)
	-> <prop-descriptor>
	-> undefined
```


### `parentCall(..)`

Get parent method and call it
```
parentCall(<prototype>, <name>, <this>)
	-> <result>
	-> undefined

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

Special case: call the parent callable implementation
```
parentCall(<prototype>, '__call__', <this>)
	-> <result>
	-> undefined
```

See [`parent(..)`](#parent) and [`sources(..)`](#sources) for more details.


### `mixin(..)`

_Mixin_ objects into a prototype chain
```
mixin(<base>, <object>, ..)
	-> <base>
```

This will link the base `.__proto__` to the last _mixin_ in chain, 
keeping the prototype visibility the same.

This will copy the content of each input object without touching the 
objects themselves, making them fully reusable.


### `mixins(..)`

Get matching mixins
```
mixins(<base>, <object>)
mixins(<base>, [<object>, ..])
mixins(<base>, <object>, <callback>)
mixins(<base>, [<object>, ..], <callback>)
	-> list
```

```
callback(<match>, <object>, <parent>)
	-> STOP 
	-> undefined
	-> <value>
```

See [`sources(..)`](#sources) for docs on `callback(..)`


### `hasMixin(..)`

Check if _base_ object has _mixin_
```
hasMixin(<base>, <mixin>)
	-> <bool>
```


### `mixout(..)`

Remove the _first_ match matching input _mixin_ from _base_ 
of _base_
```
mixout(<base>, <object>, ..)
mixout(<base>, 'first', <object>, ..)
	-> <base>
```

Remove _all_ occurrences of each matching input _mixin_ from _base_
```
mixout(<base>, 'all', <object>, ..)
	-> <base>
```

This is the opposite of `mixin(..)`


### `mixinFlat(..)`

Mixin contents of objects into one _base_ object
```
mixinFlat(<base>, <object>, ..)
	-> <base>
```
This is like `Object.assign(..)` but copies property descriptors rather 
than property values.


### `RawInstance(..)`

Make a raw (un-initialized) instance
```
RawInstance(<context>, <constructor>, ..)
	-> <object>
```

`RawInstance(..)` will do the following:
- Create an instance object
	- get result of `.__new__(..)` if defined, or
	- if prototype is a function or `.__call__(..)` is defined, create a 
	  wrapper function, or
	- if constructor's `.__proto__` has a `.__rawinstance__(..)` use it
	  to create an instance, or
	- if constructor's `.__proto__` is a function (constructor) use it 
	  to create an instance, or
	- use `{}`.
- Link the object into the prototype chain


_Un-initialized_ means this will not call `.__init__(..)`


`RawInstance(..)` can be called with and without `new`.


### `Constructor(..)` / `C(..)`

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>
```

`Constructor(..)` essentially does the following:
- Creates a _constructor_ function,
- Sets constructor `.name` and `.toString(..)` for introspection,
- Creates `.__rawinstance__(..)` wrapper to `RawInstance(..)`
- Sets constructor `.__proto__`, `.prototype` and `.prototype.constructor`,
- Mixes in _constructor-mixin_ if given.

The resulting _constructor_ function when called will:
- call constructor's `.__rawinstance__(..)` if defined or `RawInstance(..)` 
  to create an instance,
- call instance's `.__init__(..)` if present.


Note that `Constructor(<name>, <prototype>)` is intentionally set as default
instead of having the _parent-constructor_ as the last argument, this is 
done for two reasons:
- The main cause to inherit from a constructor is to extend it,
- In real code the `Constructor(<name>, <prototype>)` is more common than
  empty inheritance.


Shorthand to `Constructor(..)`
```
C(<name>, ..)
	-> <constructor>
```


`Constructor(..)` / `C(..)` can be called with and without `new`.



## Utilities

### `normalizeIndent(..)` / `normalizeTextIndent(..)`

Align _code_ to shortest leading white-space
```
normalizeIndent(<text>)
normalizeIndent(<text>, <tab-size>)
normalizeIndent(<text>, <tab-size>, <keep-tabs>)
	-> <text>
```

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

`tab_size` defaults to `object.TAB_SIZE`

`keep_tabs` defaults to `object.KEEP_TABS`


A shorthand to `normalizeIndent(..)` optimized for text rather than code
```
normalizeTextIndent(..)
	-> <text>
```

This ignores `object.KEEP_TABS` and `keep_tabs` is 0 by default.


### `match(..)`

Test if the two objects match in attributes and attribute values
```
match(base, obj)
	-> bool
```

This relies on first level object structure to match the input object, for 
a successful match one of the following must apply:
- object are identical

or:
- `typeof` matches _and_,
- attribute count matches _and_,
- attribute names match _and_,
- attribute values are identical.



## 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:
```javascript
// 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:
```javascript
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](./LICENSE)

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


<!-- vim:set ts=4 sw=4 spell : -->