# object.js

_object.js_ provides a set of tools for making and maintaining object
constructors and for managing their inheritance relations.


This is an alternative to the ES6 `class` syntax in JavaScript and provides 
several advantages:  
- Simple way to define instance and "class" 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__(..)`)
- 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



## Installation

```bash
$ 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')
```


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

```javascript
var B = object.Constructor('B', {__proto__: A.prototype})

var C = object.Constructor('C', Object.create(B.prototype))
```

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

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


### Inheritance
```javascript
//
//    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', {
    // inherit from Base...
    __proto__: Base.prototype,

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

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

```


### Callable instances

```javascript
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.


### Low level constructor

```javascript
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.


## 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 flaw -- it can't distinguish 
between two references to the same method in a chain and will always 
return the first, so the first case is preferable. This issue can't be 
resolved as this case has no information on the prototype containing the 
reference, but these cases should not be very common._


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>
```

_EXPERIMENTAL: a shorthand to this is defined as `Constructor.__rawinstance__(context, ..)`_

Define an object constructor
```
Constructor(<name>, <prototype>)
Constructor(<name>, <class-prototype>, <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.


## License

[BSD 3-Clause License](./LICENSE)

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

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