hidden-state

Attach hidden state to object instances.

Example

import { hiddenState } from 'hidden-state';

const [getState, initState, hasState] = hiddenState('Point');

class Point {

  constructor(x, y) {
    initState(this, { x, y });
  }

  toString() {
    let { x, y } = getState(this);
    return `<${ x }:${ y }>`;
  }

  add(point) {
    let { x: x1, y: y1 } = getState(this);
    let { x: x2, y: y2 } = getState(point);
    return new Point(x1 + x2, y1 + y2);
  }

  static isPoint(obj) {
    return hasState(obj);
  }

}

Install

npm install hidden-state

API

hiddenState(typeName?)

Returns an array containing functions that can be used to access the hidden state of an object. The optional typeName argument is used to customize TypeError messages.

const [getState, initState, hasState] = hiddenState('MyType');

The following functions are returned:

getState(obj)

Returns the hidden state associated with the specified object. If the object does not have hidden state then a TypeError is thrown.

initState(obj, state)

Initializes the hidden state for an object. A TypeError is thrown if state is undefined. An Error is thrown if hidden state has previously been initialized for the object.

hasState(obj)

Returns a boolean value indicating whether the object has associated hidden state.