It's not quite clear to me why you'd use this over something more established such as protobuf, thrift, flatbuffers, cap n proto etc.
What if you are reading from a service which already have an established API?
It's not like you can just tell them to move to protobuf.
Those care about quickly sending compact messages over the network, but most of them do not create a sparse in-memory representation that you can read on the fly. Especially in javascript.
This lib keeps the compact representation at runtime and lets you read it without putting all the entities on the heap.
Cool!