sacrosanct

Module for creating immutable JavaScript objects using ES2015 Proxies.

Requires Node.js 6+

Why?

The purpose of this module is to protect shared objects from being mutated as you pass them around without freezing the original objects. Great example of this would be for use in a redux-like application where application state should only be mutated by dispatching actions that ultimately return brand new states.

Wait, why not just use Object.freeze()?

You could! Object.freeze() would be appropriate for the use case that you had an object you wanted to freeze forever and never touch again. But what if you had an object that you wanted to be able to safely share with others, but also retain the ability to make runtime changes yourself? This is where using Proxy comes into play. The original object passed into sacrosanct() remains mutable, thus allowing you to make whatever changes you'd like to the target object in your own module scope, while restricting access for others by exporting the returned frozen object.

Installation

npm install sacrosanct

Usage

const freeze      = require('sacrosanct');
const frozen      = freeze({ cantChangeMe: true });

frozen.cantChangeMe = false;

console.log( frozen.cantChangeMe ); // true

You can configure frozen objects to be noisy and throw on mutations as well. Just pass true as the second argument to turn on strict mode (for use in conjunction with use strict).

'use strict';

const freeze      = require('sacrosanct');
const frozen      = freeze( { cantChangeMe: true }, true );

frozen.cantChangeMe = false; // TypeError: 'set' on proxy: trap returned falsish for property 'cantChangeMe'