Input and output

Input provides data when an actor is created.

const greetingMachine = createMachine({
  context: ({ input }: { input: { name: string } }) => ({ name: input.name })
});

const greeting = createActor(greetingMachine, {
  input: { name: 'Ada' }
}).start();

When a machine declares schemas.input (directly or through setup(...)) and the input type does not accept undefined, createActor requires the input option. Restoring a persisted snapshot does not require it.

Final output

const machine = createMachine({
  context: { result: 42 },
  initial: 'working',
  states: {
    working: { on: { finish: { target: 'done' } } },
    done: { type: 'final' }
  },
  output: ({ context }) => ({ result: context.result })
});

Read output from a completed snapshot or an invocation's done event.

Input configures one actor instance. Output reports its final result.

• An invoice actor can receive a currency and line items as input, then output the calculated total.
• A file-processing actor can receive a file key as input, then output the generated asset URL.

Actors that run indefinitely may never produce output.

TypeScript

Declare input and output schemas when they cross actor boundaries.

The output type is inferred from the root output when schemas.output is not declared. Without a root output, the type is the union of the top-level final states' output types. A declared schemas.output is authoritative and the root output is checked against it.

const machine = setup({}).createMachine({
  context: { shipped: ['sku-1'] },
  initial: 'done',
  states: { done: { type: 'final' } },
  output: ({ context }) => ({
    status: 'shipped' as const,
    skus: context.shipped
  })
});

// OutputFrom<typeof machine> is { status: 'shipped'; skus: string[] }

Input and output cheatsheet

context: ({ input }) => ({ value: input.value })
output: ({ context }) => ({ value: context.value })
createActor(machine, { input: { value: 1 } });