machine.js

  // Available variables:
  // - Machine
  // - interpret
  // - assign
  // - send
  // - sendParent
  // - spawn
  // - raise
  // - actions
  // - XState (all XState exports)
  const accessHandshake = {
    id: 'fetch',
    initial: 'requested',
    states: {
      requested: {
        invoke: {
          src: 'checkPin',
          onDone: {
            target: 'accepting'
          },
          onError: {} // Nothing
        },
        on: {
          ACCEPT: 'accepting',
          REJECT: 'rejected'
        }
      },
      accepting: {
        on: {
          RESOLVE: 'accepted',
          REJECT: 'errored'
        }
      },
      accepted: {
        invoke: {
          src: 'respond',
          onDone: {
            target: "#fetch.waiting"
          }
        }
      },
      rejected: {
        invoke: {
          src: 'respond',
          onDone: {
            target: "#fetch.waiting"
          }
        }      },
      errored: {
        invoke: {
          src: 'respond',
          onDone: {
            target: "#fetch.waiting"
          }
        }      
      }
    }
  }
  const fetchMachine = Machine({
    id: 'fetch',
    initial: 'idle',
    on: {
      DISABLE: 'idle'
    },
    states: {
      idle: {
        on: {
          ENABLE: 'initialising'
        }
      },
      initialising: {
        invoke: {
          src: 'startInterface',
          onDone: {
            target: 'waiting'
          },
          onError: {
            target: 'failed'
          }
        }
      },
      failed: {
        type: 'final'
      },
      waiting: {
        on: {
          REQUEST_RECEIVED: 'handshaking'
        }
      },
      handshaking: accessHandshake
    }
  });