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Interface-js

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Exposes a way to enforce an interface on classes.

Installation

npm install --save interface

Usage

To enforce an interface, first create a new Interface and pass it the function names that you want to enforce.

const MyInterface = Interface.create('myMethodA', 'myMethodB')

or alternatively

const MyInterface = new Interface('myMethodA', 'myMethodB')

Next, just make your class extend from the interface. Make sure you call super() within your class's constructor.

class MyClass extends MyInterface {
  constructor () {
    super()
  }

  myMethodA () {
    // ...implementation goes here
  }
}

Now, whenever you try to instantiate MyClass, the interface will be enforced.

const instance = new MyClass()
// throws a new error with the message:
// 'The following function(s) need to be implemented for class MyClass: myMethodB'

Of course, the interface is enforced on all subclasses as well.

class MySubClass extends MyClass {
  constructor () {
    super()
  }

  myMethodA () {
    // override 'myMethodA'
  }
}

const instance = new MySubClass()
// still throws an error with the message:
// 'The following function(s) need to be implemented for class MyClass: myMethodB'

Interfaces can be enforced for classes defined the old way too.

const inherits = require('util').inherits

const MyInterface = new Interface('myMethodA', 'myMethodB', 'myMethodC')

function MyClass () {
  MyInterface.call(this)
}

inherits(MyClass, MyInterface)

MyClass.prototype.myMethodA = function () {
  // implementation
}

function MySubClass () {
  MyClass.call(this)
}

// inherit prototype of parent class
inherits(MySubClass, MyClass)

MySubClass.prototype.myMethodB = function () {
  // implementation
}

var instance = new MySubClass()
// throws an error with the message:
// 'The following function(s) need to be implemented for class MyClass: myMethodC'

You can also enforce that arbitrary objects match an interface by using the isImplementedBy method.

const MyInterface = new Interface('myMethod')

class MyClass {
  myMethod () {
    // some implementation
  }
}

class MyOtherClass {
  myOtherMethod () {
    // some implementation
  }
}

const instanceA = new MyClass()
const instanceB = new MyOtherClass()

MyInterface.isImplementedBy(instanceA) // returns true
MyInterface.isImplementedBy(instanceB) // returns false