This is an experimental LevelDB plugin got Terraformer's GeoStore. Should work in the browser with browserify (thanks @calvinmetcalf).
npm install --save terraformer-geostore-leveldb leveldown
Note that it does not come bundled with leveldown by default, you need to install that too.
var LevelStore = ;var store =store: "buildings"index:;
run tests with
npm test, it will run the node and browser tests.