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https://github.com/insin/concur

Sugar for infectious JavaScript inheritance, metaprogramming & mixins
https://github.com/insin/concur

inheritance javascript metaprogramming mixins utility

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Sugar for infectious JavaScript inheritance, metaprogramming & mixins

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README 

        
# Concur [![build status](https://secure.travis-ci.org/insin/concur.png)](http://travis-ci.org/insin/concur)



Syntactic sugar for JavaScript inheritance, which takes two of the JavaScript

Functions Of The Ages (`extend()` and `inherits()`), combines their power in

a [Backbone](https://github.com/documentcloud/backbone)-style infectious

inheritance function and allows for inheritance-time metaprogramming and mixins

for those who need them.



Runs in browsers and [Node.js](http://nodejs.org).



## Install



Browser bundles export a global `Concur` variable.



* [concur.js](https://raw.github.com/insin/concur/master/concur.js)

* [concur.min.js](https://raw.github.com/insin/concur/master/concur.min.js)



Node.js:



```

npm install Concur

```

```javascript

var Concur = require('Concur')

```



## Usage



Concur is [sugar](http://en.wikipedia.org/wiki/Syntactic_sugar) for JavaScript

inheritance.



It deals with constructor functions, prototypes and prototype chains.

It does not break ``instanceof`` and constructors created with Concur will

not be ``instanceof Concur`` - it does not attempt to transplant paradigms

from other languages into JavaScript, but it *does* try to provide a

convenient means of manipulating prototypes while setting up inheritance.



Assuming the standard `inherits(child, parent)` function - which (\*deep

breath\*) puts one constructor's prototype in another constructor's prototype

chain, so objects created with the latter will have access to the former's

prototype properties when property access walks the prototype chain - you

might have an inheritance hierarchy set up something like this:



```javascript

function inherits(child, parent) {

  function F() {}

  F.prototype = parent.prototype

  child.prototype = new F()

  child.prototype.constructor = child

}



function Widget(attrs) {

  this.attrs = attrs || {}

}



Widget.prototype.isHidden = false



function Input(attrs) {

  Widget.call(this, attrs)

}

inherits(Input, Widget)



Input.prototype.inputType = null



Input.prototype.render = function(name, value) {

  return React.createElement('input', {

    type: this.inputType

  , name: name

  , value: value

  })

}



function TextInput(attrs) {

  Input.call(this, attrs)

}

inherits(TextInput, Input)



TextInput.prototype.inputType = 'text'

```



You could start sugaring this by having Concur take care of setting up

prototype inheritance and generating default constructors.



The `Concur.extend()` function returns a constructor function - either

one you provide or a default which calls the "parent" constructor in the

context of the object being created, passing along all given arguments -

which you can continue to work with as above. The `extend()` function is

attached to the resulting constructor before it is returned, so it can be

further extended from using the same API.



Setting up a prototype by augmenting a constructor's prototype

property-by-property is preferred by some as it doesn't introduce any extra

levels of nesting, and gives each property plenty of room for scanning and

documentation:



```javascript

var Widget = Concur.extend({

  constructor: function(attrs) {

    this.attrs = attrs || {}

  }

})



Widget.prototype.isHidden = false



var Input = Widget.extend()



Input.prototype.inputType = null



Input.prototype.render = function(name, value) {

  return React.createElement('input', {

    type: this.inputType

  , name: name

  , value: value

  })

}



var TextInput = Input.extend()



TextInput.prototype.inputType = 'text'

```



To further sugar this, you could pass additional properties to the

`extend()` function, which will augment the prototype for you.



You might prefer to do this only with data, rather than functions, or you

might prefer the compactness of having the entire prototype definition as

part of one statement (particularly for constructors with small

prototypes) - for demonstration purposes, this example shows the latter:



```javascript

var Widget = Concur.extend({

  isHidden: false,



  constructor: function(attrs) {

    this.attrs = attrs || {}

  }

})



var Input = Widget.extend({

  inputType: null,



  render: function(name, value) {

    return React.createElement('input', {

      type: this.inputType

    , name: name

    , value: value

    })

  }

})



var TextInput = Input.extend({

  inputType: 'text'

)}

```



### Manipulating Prototypes



The following "special" properties, or "dunder-properties" owing to the double

underscores, can be used to manipulate prototypes at inheritance time. The

manipulations they enable are performed in the order they are listed below.



#### `__meta__(prototypeProps, constructorProps)`



If a constructor's prototype properties include a dunder-meta property,

then when `extend()` is used on that constructor, dunder-meta will be

called with all property-defining objects which were passed in.



This enables you to declare constructors which can modify the prototypes of

constructors inheriting from them, at inheritance time.



Contrived example:



```javascript

function NutAllergyProtectionMeta(prototypeProps) {

   var nutIndex = prototypeProps.ingredients.indexOf('nuts')

   if (nutIndex != -1) {

      prototypeProps.ingredients.splice(nutIndex, 1)

   }

}



var Bar = Concur.extend({

  __meta__: NutAllergyProtectionMeta,



  eat: function() {

    if (this.ingredients.indexOf('nuts') != -1) {

      console.log('You eat nuts. You die.')

    }

    else {

      console.log('You feel a bit dunder-meta.')

    }

  }

})



var NougatBar = Bar.extend({

   ingredients: ['sugar', 'egg whites', 'nuts']

})

```

```

>>> var snack = new NougatBar()

>>> snack.eat()

You feel a bit dunder-meta.

```



Actual examples:



* Implementing basic Django-style declarative models:

  [`examples/models.js`](https://github.com/insin/concur/blob/master/examples/models.js).

* Implementing inheritance of fields from ancestor constructors and mixing in

  fields from other constructors at the same time:

  [newforms' `DeclarativeFieldsMeta.js`](https://github.com/insin/newforms/blob/react/src/forms/DeclarativeFieldsMeta.js)



#### `__mixins__`



If any properties object passed to `extend()` includes a dunder-mixins

Array, each of its contents will be mixed into that properties object in the

given order.



## API



### `Concur.extend([prototypeProps[, constructorProps]])`



Creates a child constructor which inherits from the call context object

(`this`), adding the given prototype and constructor properties and

adding `extend()` as a property of the new constructor for further

extension:



* Calling `Concur.extend()` creates a "base" constructor, which inherits

  from `Object` just like any other Function.



* Calling `extend()` in the context of any other constructor creates a

  new constructor which inherits from it.



When required, constructor logic should be provided as a function -

`prototypeProps.constructor()` - otherwise, a default constructor which

calls the parent constructor with all given arguments will be created for you.



Child constructors will have a `__super__` property added to them referencing

the prototype they extend, as a convenience for accessing it when required.



Child constructors will also have an `__mro__` property added to them, which

is a list of the constructors in their inheritance chain, with the new child

constructor itself at the head of the list.



#### Special arguments



##### `prototypeProps.constructor([...])`



If provided, this function will be used as the child constructor, otherwise a

new child constructor function will be created for you.



##### `prototypeProps.__meta__(prototypeProps, constructorProps)`



If provided, this function will not be used immediately, but will be called

when further extension is done based on the constructor returned by this call

to `extend()`.



At that point, `__meta__` will be called with the property arguments passed

to `extend()` so it can customise them before they're used to set up the

inheriting constructor's prototype.



##### `prototypeProps.__mixins__` and `constructorProps.__mixins__`



If provided, the contents of this Array will be mixed in to the properties

object it's set on, in the given order.



## MIT Licensed