Finite state machines are useful for modeling complicated flows and keeping track of state. TS-FSM is a strongly typed finite state machine for TypeScript that is using promises for async operations. I'm using this state-machine as a simple replacement for Redux in some ReactJs based apps. Example here
- TypeScript native (compiles to ES6)
- Only 1 KB (minified) and zero dependencies!!!
- Hooks after state change - - async or sync callbacks
- Promises are used for async transition completion
- Generics for states and events types
- Simple tabular state machine definition
- Use with NodeJS or JS client
git clone https://github.com/eram/typescript-fsm.git cd typescript-fsm npm install npm test npm install typescript-fsm I'm modeling a "door" here. One can open the door, close it or break it. Each action is done async: when you open it goes into opening state and then resolved to opened state etc. Once broken, it reaches a final state.
Let's code it in Typescript! Note that the same code can be run in Javascript, just remove the generics.
import { t, StateMachine } from "typescript-fsm"; // these are the states and events for the door enum States { closing = 0, closed, opening, opened, broken }; enum Events { open = 100, openComplete, close, closeComplete, break }; // lets define the transitions that will govern the state-machine const transitions = [ /* fromState event toState callback */ t(States.closed, Events.open, States.opening, onOpen), t(States.opening, Events.openComplete, States.opened, justLog), t(States.opened, Events.close, States.closing, onClose), t(States.closing, Events.closeComplete, States.closed, justLog), t(States.closed, Events.break, States.broken, justLog), t(States.opened, Events.break, States.broken, justLog), t(States.opening, Events.break, States.broken, justLog), t(States.closing, Events.break, States.broken, justLog), ]; // initialize the state machine const door = new StateMachine<States, Events>( States.closed, // initial state transitions, // array of transitions ); // transition callbacks - async functions async function onOpen() { console.log("onOpen..."); return door.dispatch(Events.openComplete); } async function onClose() { console.log("onClose..."); return door.dispatch(Events.closeComplete); } // synchronous callbacks are also ok function justLog() { console.log(`${States[door.getState()]}`); } // we are ready for action - run a few state-machine steps... new Promise(async (resolve) => { // open the door and wait for it to be opened await door.dispatch(Events.open); door.getState(); // => States.opened // check if the door can be closed door.can(Events.close); // => true // break the door async door.dispatch(Events.break).then(() => { // did we get to a finite state? door.isFinal(); // => true }); // door is now broken. It cannot be closed... try { await door.dispatch(Events.close); assert("should not get here!"); } catch (e) { // we're good } // let the async complete setTimeout(resolve, 10); });Check out the test code - a class that implements a state machine with method binding, method params and more transitions. 100% coverage here!
Comments and suggestions are welcome.