# object.js

object.js provides a set of tools for constructing and maintaining object
constrictors and for managing their inheritance relations.


This is an elternative to the ES6 `class` syntax in JavaScript and provides 
several advantages:  
- simple way to define normal and class methods, properties and attributes,
- uniform and minimalistic definition syntax based on basic JavaScript 
  object syntax no special cases or special syntax,
- _transparantly_ based on _JavaScript's_ prototypical inheritance model,
- more granular instance construction (a-la _Python's_ `.__new__(..)` 
  and `.__init__(..)` methods)
- less restrictive:
    - `new` is optional
    - all input components are reusable

Disadvantages compared to the `class` syntax:  
- no _sytactic sugar_
- a slightly more complicated `super` call method


## Usage

```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.prototypes` 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
// NOTE: we could simply use A() or new A() here but that would call
//      the active constructors if they are defined which might not be
//      desirable at definition time...
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.parent(this.__init__, this).call(this)
        this.item_attr = 'instance attribute value'
    },
})

```


### Callable instances
```javascript
// callable instance constructor...
var Action = object.Constructor('Action',
    // Define a constructor as a function...
    //
    // The first argument is allways the external call context, like
    // normal this, but here we have two contexts:
    //  - internal (this)       -- the instance (this)
    //  - external (context)    -- call context
    //
    // NOTE: if the prototype is explicitly defined as a function then
    //      it is the user's responsibility to call .__call__(..) method
    //      (see below)
    function(context, ...args){
        // return the instance...
        return this
    })

var action = new Action()

action()


// a different way to do the above...
var Action2 = object.Constructor('Action2', {
    // 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.
    //
    // Contexts:
    //  - internal (this)       -- the instance
    //  - external (context)    -- call context
    //
    // NOTE: this is not called if a user defines the prototype as a function
    //      (see above)
    __call__: function(context, ...args){
        return this
    },
})

```

### Low level constructor
```javascript
var LowLevel = object.Constructor('LowLevel', {
    // Low level instance constructor...
    //
    // Contexts:
    //  - internal (this)       -- .prototype
    //  - external (context)    -- call context
    //
    // NOTE: if this is defined the return value is used as the instance
    // NOTE: this has priority over the callable protocols above, thus
    //      the user must take care of both the prototype as function and
    //      prototype.__call__(..)...
    __new__: function(context, ...args){
        return {}
    },
})

```

## Components

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

```
parent(<method>, <this>)
parent(<method>, <name>, <this>)
    -> <parent-method>
```

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

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

```
Constructor(<name>, <prototype>)
Constructor(<name>, <class-prototype>, <prototype>)
    -> <constructor>
```



## License

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

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

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