Generated by XState Viz: https://xstate.js.org/viz

machine.js

const timer = Machine(
  {
    id: "timer",
    initial: "idle",
    context: {
      timer: 0
    },
    states: {
      idle: {
        on: {
          START: "running"
        }
      },
      running: {
        invoke: {
          id: "counting",
          src: (context) => (callback) => {
            const intervalId = setInterval(() => callback("COUNT"), 1000);
            return () => clearInterval(intervalId);
          }
        },
        on: {
          STOP: "idle",
          COUNT: {
            actions: assign({
              timer: (context) => context.timer + 1
            })
          }
        }
      }
    },
    on: {
      RESET: {
        target: "idle",
        actions: ["resetTimer"]
      }
    }
  },
  {
    actions: {
      resetTimer:assign({
        timer: 0
      })
    }
  }
);