Fixd NPM | npm.io

Fixd

Fixd is a JavaScript library for creating reference-free, immutable (frozen) objects. It supports immutability on all native types, including deeply nested objects and arrays.

The use-case Fixd was built around is "locking" reusable fixtures to prevent mutations, an in-turn, side-effects during testing.

Installation

npm i fixd --save

Quick Start

'use strict'
const fixd = require('fixd')

// Add a new object
fixd.foo = { 
  fizz: 'buzz', 
  baz: { 
    quz: 'baz' 
  } 
}

// Access object
fixd.foo // -> { fizz: 'buzz', baz: { quz: 'baz' } }

// Throws error, prevents mutations
foo.fizz = 'bazz' // -> ERROR: Cannot assign to read only property

Note: While Object.freeze will prevent modifications, use strict must be applied to the document in order to throw an error on attempted mutation.

Creating New Instances

Because the objects are frozen, Fixd provides the create method for returning a new, modified instance.

fixd.create('foo', (foo) => {
  foo.fizz = 'bazz'
  return foo
}) // -> { fizz: 'bazz', baz: { quz: 'baz' } }

The above will not modify the foo object, it will return a new, reference-free, frozen instance of the object based on the modification performed in the callback.