v4.7.0

• 🐌 If a subscriber/listener subscribes to a service that is already running, it will now receive the current state upon subscription. #814
• 🆙 The new escalate() action creator escalates custom error events to a parent machine, which can catch those in the onError transition:

import { createMachine, actions } from 'xstate';
const { escalate } = actions;

const childMachine = createMachine({
  // ...
  // This will be sent to the parent machine that invokes this child
  entry: escalate({ message: 'This is some error' })
});

const parentMachine = createMachine({
  // ...
  invoke: {
    src: childMachine,
    onError: {
      actions: (context, event) => {
        console.log(event.data);
        //  {
        //    type: ...,
        //    data: {
        //      message: 'This is some error'
        //    }
        //  }
      }
    }
  }
});

• ❓ You can now specify undefined as the first argument for machine.transition(...), which will default to the initial state:

lightMachine.transition(undefined, 'TIMER').value;
// => 'yellow'

• 🤝 Services (invoked machines) are now fully subscribable and can interop with libraries that implement TC39 Observbles like RxJS. See https://xstate.js.org/docs/recipes/rxjs.html for more info.

• 🆔 When a service is invoked, it has a uniquely generated sessionId, which corresponds to _sessionid in SCXML. This ID is now available directly on the state object to identify which service invocation the state came from: state._sessionid #523

• ⚙️ The original config object passed to Machine(config) (or createMachine(config)) is now the exact same object reference in the resulting machine.config property.

• 🎰 The createMachine() factory function now exists and is largely the same as Machine(), except with a couple differences:

  • The generic type signature is <TContext, TEvent, TState> instead of <TContext, TStateSchema, TEvent>.
  • There is no third argument for specifying an initial context. Use .withContext(...) on the machine or return a machine with the expected context in a factory instead.

• 🛑 Event sent to a stopped service will no longer execute any actions, nor have any effect. #735

• 🚸 The invoked actors are now directly available on state.children.

• ✍️ Plain strings can now be logged in the log() action creator:

entry: log('entered here', 'some label')

• 🚄 Transitions are now available on state.transitions, which is an array of transition objects that detail exactly which transitions were enabled to transition to this state. This will be ignored in serialization.
• ⏩ New action creator: forwardTo() https://xstate.js.org/docs/guides/actions.html#forward-to-action
• ➕ Assigners now have a third meta argument passed in, which contains meta data such as the state and the original action
• *️⃣ New event type: the wildcard! https://xstate.js.org/docs/guides/transitions.html#wildcard-descriptors

const quietMachine = Machine({
  id: 'quiet',
  initial: 'idle',
  states: {
    idle: {
      on: {
        WHISPER: undefined,
        // On any event besides a WHISPER, transition to the 'disturbed' state
        '*': 'disturbed'
      }
    },
    disturbed: {}
  }
});

quietMachine.transition(quietMachine.initialState, 'WHISPER');
// => State { value: 'idle' }

quietMachine.transition(quietMachine.initialState, 'SOME_EVENT');
// => State { value: 'disturbed' }

• 📲 New action creator: respond() https://xstate.js.org/docs/guides/actions.html#respond-action
• ✅ New typechecking feature: Typestates https://xstate.js.org/docs/guides/typescript.html#typestates-coming-soon
• 📄 SCXML event metadata is now available on state._event and also in action/guard/etc. meta under _event. https://www.w3.org/TR/scxml/#InternalStructureofEvents