fn-machine

fn-machine

A tiny, functional, state machine utility

install

npm install --save fn-machine

usage

fn-machine consists of 3 functions. The first two are used to define a machine:

machine([State], 'initialState', initialContextObj, stateChangeCallback, loggerFn)

state('name', transitionsObj, enterFunction, exitFunction)

The third function is what would traditionally be called a send() function. This function is returned whenever machine(...) is called.

Setting up a machine

// import the setup functions
import {machine, state} from 'fn-machine';

// initial context object
const initialContext = {
  loading: false,
  users: []
}

function loadUsers() {
  // simulate a network request
  setTimeout(() => {
    // once the request completes, we can call `myMachine` (the 'send' function).
    myMachine('loaded', {users:['foo', 'bar']})
  }, 1000);
}

// initialize a machine
const myMachine = machine([
  state('initial', {
    // each method on this object represents a transition for this particular state.
    loadData: (detail, context) => {
      // a transition method should return the new state, as well as the optional context.
      // here we return {state:'loadingData'} to signify we want the state to now be 'loadingData', and
      // that the context.loading property should be true.
      return {
        state:'loadingData',
        context: {...context, ...{loading: true}}
      }
    }
  }),
  state('loadingData', {
    loaded: (detail, context) => {
      return {
        state: 'loadedData',
        context: {...context, ...detail, ...{loading: false}}
      }
    }
  }, context => {// call loadUsers when this state is entered
    loadUsers();
  }),
  state('loadedData', {}) // 'loaded' is an empty state. There are no transitions.
], 'initial', initialContext, newState => {
  console.log('myMachine state changed:', newState.state, newState.context);
}, console.log);// pass an optional logger function

As you can see in the loadUsers() function above, we invoke the third function provided by fn-machine, which is the send function. The send function takes a string as the first parameter, which is the name of a transition we'd like to invoke, and optionally a detail object, which might contain some data we want the machine to work with.

More examples

There is an example in this repo, or you can play around with this codepen that shows a basic integration with LitElement.

Contributing

Yes! PR's are welcome. Tests are written in mocha. Run with npm run test or yarn test. Typechecking is provided by typescript via JSDoc annotations.