Event Step

The Event Step lets you define custom logic in response to subscribed events and at the same time trigger other steps by emitting new events. It enables communication between different parts of your flow.

Config

The following properties are specific to the Event Step, in addition to the common step config.

Prop	Type	Description
input	`string[]`	This is used for input validation. For TypeScript/JavaScript steps, it uses zod schemas. For Python steps, it uses Pydantic models. This validates the input before executing the step handler.

The following examples showcase how to configure an Event Step

import { EventConfig, StepHandler } from 'motia'
import { z } from 'zod'
 
const inputSchema = z.object({
  message: z.string()
})
 
type Input = typeof inputSchema
 
export const config: EventConfig<Input> = {
  type: 'event',
  name: 'stepA',
  description: 'Hello from Step A',
  subscribes: ['pms.start'],
  emits: ['pms.stepA.done'],
  input: inputSchema,
  flows: ['parallel-merge'],
}
 
export const handler: StepHandler<typeof config> = async (input, { emit, logger }) => {
  logger.info('Processing message:', input.message)
 
  await emit({
    topic: 'pms.stepA.done',
    data: {
      result: `Processed: ${input.message}`
    }
  })
}

Example

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Event Step

Config

Example

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