An Event Sourcing system based only on Typescript types.
Inspired by this Functional Event Sourcing Decider blog post.
Event Sourcing TLDR: don't store the final state of an object, store the command/events that led to that state.
The Event Sourcing system is designed to follow the following steps at each clock:
- receive an input
- process the received input through a decider
- the decider produces a list of events
- each event is processed by a fold function to produce a new state
- once all events are folded, the final state is returned
A clock is triggered by command reception.
Note: in the blog post proposal, this is a pure functional core system. The application layer is responsible for:
- translating external commands/events into internal commands
- observing output events and triggering the associated side effects
- Press
.or change the domain fromgithub.comtogithub.dev(maintaining the URL) to open the editor. - Open /src/index.ts
- Let few minutes for the Typescript engine to steam up in the browser.
- Hover with the mouse on the example types to observe how the system works.
This is a proof of concept, not a fully polished library.
It is just here to demonstrate how Typescript can be used to model an Event Sourcing system using types only.