With persistent changes, you leave behind a trail of breadcrumbs that lets you time travel back to any point in your data's past. Whether or not you choose to keep track of these changes is entirely up to you. The need to do this depends on what you're building. For example, it might be useful to be able to roll back changes made to immutable data collections.

Let's implement an abstraction that wraps an Immutable.js collection, augmenting it with history tracking capabilities:

import { List, Stack } from 'immutable';

// Names of List and Map methods that perform
// persistent changes. These are the methods that
// we want to build history from.
const persistentChanges = [
  'set',
  'delete',
  'deleteAll',
  'clear',
  'update',
  'merge',
  ...
];

// Where the history for a given collection is stored.
const mutations = new WeakMap();

// Defines proxy behavior for collection instances.
// It's a way to trap method calls and redirect them
// to instances in the...