Monolite is a simple, type-safe, Structural-Sharing library.

It was originally written for usage in Redux reducers, but can be used anywhere you want to preserve an object immutability.

ImmutableJS is not able to infer type on sub-state-trees as it uses strings to define sub-tree to update:

state.set(['some', 'nested', 'property'], 42);

Monolite, on its side, uses accessor functions to get the target node of the state tree to update:

set(state, _ =>, 42);

This allows TypeScript to do static analysis and completion on the sub-state type, and type of the updated value.

The library uses ES6 Proxies under-the-hood to analyze the accessor function. These functions, though, can be statically resolved, using a Babel Plugin, permitting to target older browsers not supporting Proxy.