IndexedDB API on node.js will be very useful for some app.
Why IndexedDB is not available in node.js?
IndexedDB API does not depend on DOM, even though it does use some DOM error and event style.
It's possibly because IndexedDB is part of a different body of standards. Node.js is just ECMAScript (via Google's V8) along with their own API. Also, it may not help that IndexedDB is still in "Draft."
But, more likely it's for the same reason Node.js doesn't offer any database drivers: it's not trying to solve those problems. It's just trying to offer the APIs that assist someone who does want to solve and implement them.
And, for that, it appear at least one such project has already started: indexeddb-js
. But, also have a look through IndexedDB in the NPM Registry.