In my last post, I had introduced the polyfill for IndexedDB that I was working on. IndexedDB is not yet supported on all browsers. Firefox, Chrome and Internet Explorer have implementations of IndexedDB while Safari and Opera still support WebSql. The IndexedDB specifications is also at its final stages and most browsers should have a native implementation of IndexedDB soon.
However, a client side database technology can make web apps very powerful and I thought that it would be a good idea to bridge the gap between IndexedDB and WebSql.
The polyfill exposes IndexedDB like API and uses the underlying WebSql to actually store data. This enables web applications to start using IndexedDB APIs across all the major browsers. The examples using the shim work on browsers and even devices like iPad or iPhone.
Including the Polyfill
<script type = "text/javascript" src = "http://nparashuram.com/IndexedDBShim/indexeddb.shim.js"></script>
To use the polyfill, simply link or include the indexeddb.shim.js file. The polyfill assigns window.indexedDB to be window.mozIndexedDB, window.webkitIndexedDB or window.msIndexedDB is any of those implementations are available. If no implementation is available, the polyfill kicks in and assigns window.shimIndexedDB to window.indexedDB. Hence, web applications can start using window.indexedDB as the starting point for all database operations.
To force the shim to be used, add the following statement.
window.shimIndexedDB && window.shimIndexedDB.__useShim();
The source is on github at http://github.com/axemclion/IndexedDBShim.
Libraries Tested
The polyfill is based on the IndexedDB specification and hence should work with any library that requires IndexedDB. Some of the libraries that were tested with the polyfill include the following
- JQuery-IndexedDB plugin - See example
- LINQ API for IndexedDB LINQ2IndexedDB
- PouchDB Examples - See examples
- DB.JS library - See Examples
Specification compliance
Almost all features in the IndexedDB specifications are supported by the polyfill except the following.
- Issue 1: The keys are not encoded properly and numbers are currently sorted like strings. Hence, 1 and 100 come before 2.
- Issue 2: Version Transactions are currently non-blocking. Hence, if you try to read a database when a version transaction is in progress, a race condition occurs and the results are non-deterministic.
- Issue 3: Transaction abort is not currently supported.
I am planning to follow up this post with an article that explains how the polyfill works under the covers. You can follow my work on IndexedDB here.
