Internal-data NPM

internal-data

Description

Private properties implementation using WeakMap as described on MDN - Private Properties.

Synopsis

TypeScript with WeakMap

Actually this library does nothing more than exporting an interface for TypeScript. This interface just extends WeakMap by overriding its get() method to return I instead of I | undefined, because data should already be set in constructor.

There is no need to do type assertion in every method to get internal data.

import { InternalDataInterface } from 'internal-data';

const internalData: InternalDataInterface<MyClass, Internal> = new WeakMap();

type Internal = { password: string };

class MyClass {
  name: string;

  constructor(name: string, password: string) {
    const internal: Internal = { password };
    internalData.set(this, internal);
    this.name = name;
  }

  checkPassword(password: string): boolean {
    const internal = internalData.get(this);
    return internal.password === password;
  }
}

const object = new MyClass('George', '1234');

const name     = object.name;                  // -> George
const password = object.password;              // -> TYPESCRIPT ERROR
const isValid  = object.checkPassword('1234'); // -> true

JavaScript with Function Interface

import InternalData from 'internal-data';

const getInternal = InternalData.getFunction();

class MyClass {
  constructor(name, password) {
    const internal = getInternal(this);
    this.name = name;
    internal.password = password;
  }

  checkPassword(password) {
    const internal = getInternal(this);
    return internal.password === password;
  }
}

const object = new MyClass('George', '1234');

const name     = object.name;                  // -> George
const password = object.password;              // -> Undefined
const isValid  = object.checkPassword('1234'); // -> true

JavaScript with Object Interface

import InternalData from 'internal-data';

const internalData = new InternalData(); // eslint-disable-line no-use-before-define

class MyClass {
  constructor(name, password) {
    const internal = internalData.get(this);
    this.name = name;
    internal.password = password;
  }

  checkPassword(password) {
    const internal = internalData.get(this);
    return internal.password === password;
  }
}

const object = new MyClass('George', '1234');

const name     = object.name;                  // -> George
const password = object.password;              // -> undefined
const isValid  = object.checkPassword('1234'); // -> true

Details

To access private properties of the object use getInternal(this) method. It returns an object to store private attributes of given object (In this case it is It is this)