XState: типизированные конечные автоматы

import { createMachine, assign } from "xstate";

type TrafficContext = { count: number };
type TrafficEvent =
  | { type: "TURN_GREEN" }
  | { type: "TURN_YELLOW" }
  | { type: "TURN_RED" };

const trafficMachine = createMachine({
  types: {} as { context: TrafficContext; events: TrafficEvent },
  id: "traffic",
  initial: "red",
  context: { count: 0 },
  states: {
    red:    { on: { TURN_GREEN: "green" } },
    green:  { on: { TURN_YELLOW: "yellow" } },
    yellow: { on: { TURN_RED: "red" } },
  },
});

const machine = createMachine({
  types: {} as { context: TrafficContext; events: TrafficEvent },
  // ...
  entry: assign({ count: 0 }),
  on: {
    TURN_GREEN: {
      actions: assign(({ context }) => ({ count: context.count + 1 })),
    },
  },
});

import { useMachine } from "@xstate/react";

function TrafficLight() {
  const [state, send] = useMachine(trafficMachine);
  // state.value: "red" | "green" | "yellow"
  // send: (event: TrafficEvent) => void
  return <button onClick={() => send({ type: "TURN_GREEN" })}>Go</button>;
}

const machine = createMachine({
  types: {} as { context: TrafficContext; events: TrafficEvent },
  states: {
    red: {
      on: {
        TURN_GREEN: {
          guard: ({ context }) => context.count < 10, // context: TrafficContext
          target: "green",
        },
      },
    },
  },
});

import { setup } from "xstate";
const machine = setup({
  types: {} as { context: TrafficContext; events: TrafficEvent },
  actions: {
    logTransition: ({ context, event }) => {
      console.log(context.count, event.type);
    },
  },
}).createMachine({ /* ... */ });

states: {
  ui: {
    type: "parallel",
    states: {
      modal: { initial: "closed", states: { closed: {}, open: {} } },
      tooltip: { initial: "hidden", states: { hidden: {}, visible: {} } },
    },
  },
}

const [state] = useMachine(trafficMachine);
if (state.matches("green")) {
  // TypeScript knows we're in the green state
}

import { inspect } from "@xstate/inspect";
inspect({ iframe: false }); // opens state machine inspector