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🔩 A relentless key-value store for the browser.
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ImmortalDB is a resilient key-value store for the browser.

ImmortalDB is the best way to store persistent key-value data in the browser. Data saved to ImmortalDB is redundantly stored in Cookies, IndexedDB, LocalStorage, and SessionStorage, and relentlessly self heals if any data therein is deleted or corrupted.

For example, clearing cookies is a common user action, even for non-technical users. And browsers will unceremoniously delete IndexedDB, LocalStorage, and/or SessionStorage without warning under storage pressure.

ImmortalDB is resilient in the face of such events.

In this way, ImmortalDB is like Evercookie, but

  1. Is actively maintained and well documented.

  2. Provides a simple, modern, Promise-based API.

  3. Strikes an equitable balance between reliability and respect for the user. Data is stored reliably but can also be voluntarily purged if the user designedly clears cookies and application storage.

  4. Doesn't use nefarious exploits nor deprecated third party plugins like Flash, Silverlight, or Java. Only standard, ratified HTML5 APIs are used.

  5. Doesn't vandalize performance or the user experience. For example, Evercookie's CSS History Knocking can beget a deluge of background HTTP requests, and loading Silverlight or Flash can raise unsought permission modals or thrash the user's disk.

How ImmortalDB works.

When you store a key-value pair in ImmortalDB, that key and value are saved redundantly in the browser's cookies, IndexedDB, LocalStorage, and SessionStorage data stores.

When a value is retrieved via its key, ImmortalDB

  1. Looks up that key in every data store.
  2. Counts each unique returned value.
  3. Determines the most commonly returned unique value as the 'correct' value.
  4. Returns this correct value.

Then ImmortalDB self-heals: if any data store(s) returned a value different than the determined correct value, or no value at all, the correct value is rewritten to that store. In this way, consensus, reliability, and redundancy is maintained.



ImmortalDB's API is simple. To store a value, use set(key, value):

import { ImmortalDB } from 'immortal-db'

await ImmortalDB.set('key', 'value')

key and value must be DOMStrings. ImmortalDB.set(key, value) also always returns value, so it can be chained or embedded, like

const countPlusOne = (await ImmortalDB.set('count', numberOfClowns)) + 1


To retrieve a value, use get(key, default=null):

const value = await ImmortalDB.get('key', default=null)

get() returns the value associated with key, if key exists. If key doesn't exist, default is returned. key must be a DOMString.


Finally, to remove a key, use remove(key):

ImmortalDB.set('hi', 'bonjour')
console.log(await ImmortalDB.get('hi'))  // Prints 'bonjour'.

await ImmortalDB.remove('hi')

console.log(await ImmortalDB.get('hi'))  // Prints 'null'.

key must be a DOMString.

Data Stores

The data stores that ImmortalDB stores data in can also be configured. For example, to only store data reliably in cookies and LocalStorage:

import { ImmortalStorage, CookieStore, LocalStorageStore } from 'immortal-db'

const stores = [CookieStore, LocalStorageStore]
const db = ImmortalStorage(stores)

await db.set('key', JSON.Stringify({1:1}))

Available stores are

  • CookieStore -> Keys and values are stored in document.cookie.
  • IndexedDbStore -> Keys and values are stored in window.indexedDB.
  • LocalStorageStore -> Keys and values are stored in window.localStorage.
  • SessionStorageStore -> Keys and values are stored in window.sessionStorage.

New storage implementations can easily be added, too; they need only implement the methods get(key, default), set(key, value), and remove(key).


Installing ImmortalDB with npm is easy.

$ npm install immortal-db

Or include dist/immortal-db[.min].js and use window.ImmortalDB directly.

    <script src="immortal-db.min.js"></script>
      ;(async () => {
        const db = ImmortalDB.ImmortalDB
        await db.set('hi', 'lolsup')

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