IndexedDB: the good parts



photo of Nolan Lawson
squarespace pouchdb

A story about offline storage

2010: Android was young


  • 440k+ downloads
  • 9,700+ reviews
  • 4.8 stars
  • Top 10 in category "Entertainment"

Why was Pokédroid so popular?

Many alternatives on the web

  • Bulbapedia
  • Marriland
  • Serebii
  • GameFAQs

What Pokédroid had that no others had:


It's so nice to be able to be on the road playing Pokémon and having a quick reference without all the large guidebooks.

– Google Play review

3.5MB SQLite database

2011: Pokédroid DMCA'd

  • Publishing to app store asserts IP ownership
  • Nintendo wary of apps
  • Web sites okay

In 2011, you could not build Pokédroid using web technology alone.

2009: LocalStorage API

  • Strings only
  • Synchronous
  • Key-value only
  • Capped at 5MB

2007-2010: WebSQL Database API

  • Thin layer on SQLite
  • Asynchronous
  • Nearly unlimited storage
  • Killed by Mozilla and Microsoft

2010-present: IndexedDB

  • NoSQL document store
  • Many ideas borrowed from WebSQL:
    • Asynchronous
    • Nearly unlimited storage
    • Transactional (auto-committing)
    • Security (per origin)

2010-present: IndexedDB (cont.)

  • Storage engine agnostic
    • Chrome: LevelDB
    • IE/Edge: JetDB
    • Firefox: SQLite
    • Safari: SQLite (different impl.)

Bad parts

Bad part #1: the API

Solution: use a wrapper

  • Dexie
  • LocalForage
  • PouchDB
  • YDN-DB
  • indexeddb-promised


Bad part #2: browser support

Solution: use a wrapper

  • PouchDB
  • LocalForage
  • YDN-DB
  • Dexie w/ IndexedDBShim

PouchDB support

PouchDB blob support

Bad part #4: performance

Solution: use a web worker

IDB in a worker

  • Operative.js
  • Catiline.js
  • promise-worker
  • PouchDB "worker" adapter


  • No Safari worker support for IDB/WebSQL
  • Solution: pseudo-worker

Bad part #4: WKWebView support


  • Used in hybrid apps: Cordova/PhoneGap/Ionic
  • Used in imposter iOS browsers: Chrome/Firefox/Opera
  • "Upgrade" to classic UIWebView
  • WebSQL unsupported, IDB is Apple's version
  • WK stands for "works, kinda"

Solution: FruitDOWN

  • Implementation of LevelDOWN over IDB
  • Works in all IDB impls (including Apple's)
  • PouchDB adapter
  • Barely performant, gets the job done

Another solution: SQLite Plugin (sigh)

  • Cordova plugin
  • WebSQL-esque impl over native SQLite
  • Performance is bad (serialization tax)
  • Buggy (doesn't pass Pouch test suite)
  • Doesn't fix imposter iOS browsers

WKWebView situation is awful. No good solutions. ¯\_(ツ)_/¯

Where's the good parts?

Basic tech used

  • LocalForage
  • PouchDB
  • Web workers
  • pseudo-worker (Safari)

Pokédex IDB

4.0M Chrome / 5.6M Firefox

IndexedDB: rosy future

  • Safari "modern IDB" rewrite
  • IDB v2 in Chrome/Firefox
  • IE/Edge: use the idb-iegap polyfill
IndexedDB has bad parts, but you can work around them to create amazing things.
– Nolan Lawson