abstract-class

Prevents instantiation of a parent class. Optionally defines properties that must be implemented by child classes. Imitates the functionality provided by abstract classes in languages like Java, PHP, and C++.

Installation

Requires Node.js 6.0.0 or above.

npm i abstract-class

API

The module exports a single function. This function should be called in the constructor of the class you want to declare abstract.

Parameters

1. Bindable: cls (Function): The abstract parent class.
2. obj (Object): The this variable of your object being constructed.
3. Optional: ...props (any number of: string, number, symbol, or Array thereof): The keys of the properties that a child class should implement.

Return Value

The function does not return a value.

Example

const enforceAbstractClass = require('abstract-class')

class Parent {
  constructor () {
    enforceAbstractClass(Parent, this, 'title', 'content')
  }
}

class Child extends Parent {
  get title () { return 'Title' }
}

// Throws Error: Cannot instantiate abstract class `Parent`
const parent = new Parent()

// Throws Error: `Child` must define the abstract property `content`
const child = new Child()

Constructing a Parent object fails because the class is marked abstract. Constructing a Child object also fails because Child does not define content.

You can also use the bind operator pattern:

const Abstract = require('abstract-class')

class Parent {
  constructor () {
    Parent::Abstract(this)
  }
}

// Throws Error: Cannot instantiate abstract class `Parent`
const parent = new Parent()

Limitation

If the child class provides its own constructor and fails to call the parent constructor, property abstraction will not be enforced.