Prv NPM | npm.io

prv

Private fields in Javascript

This NPM module can be used to associate private data with objects. It stores an associated object with the private data in a WeakMap, keyed on the subject. If the subject is garbage collected, so is the private data.

This module works in Node JS (v4 and up) and all browsers that have support for WeakMap (all modern browsers).

Install

npm install --save prv

Include in your app

require

const createAccessor = require('prv')
const prv = createAccessor()
// or, shorthand
const prv = require('prv')() // <-- note the double braces

import

import createAccessor from 'prv'
const prv = createAccessor()

Copy-paste

Since this module is super-small, it might be beneficial for you to just copy-paste it into your codebase verbatim:

const createAccessor = () => {
  const p = new WeakMap()
  return o => {
    if (! p.has(o)) p.set(o, {})
    return p.get(o)
  }
}

Yup, that's all there is to it!

Usage

Create an accessor function and use it to associate private data with objects. Only code that has access to the accessor function can reach the private data.

import createAccessor from 'prv'
const prv = createAccessor()

class Point {
  constructor(x, y) {
    prv(this).x = x
    prv(this).y = y
  }

  get x() {
    return prv(this).x
  }

  get y() {
    return prv(this).y
  }
}

const point = new Point(0,0)
console.info(point.x) // 0
console.info(point.y) // 0

// attempting to set x
// ignored in 'sloppy' mode
// throws TypeError in strict mode
point.x = 10