msw/src/browser/setupWorker/start/utils/createMessageChannel.ts

Seamless REST/GraphQL API mocking library for browser and Node.js.

import {
  StringifiedResponse,
  ServiceWorkerIncomingEventsMap,
} from '../../glossary'

export interface ServiceWorkerMessage<
  EventType extends keyof ServiceWorkerIncomingEventsMap,
  EventPayload,
> {
  type: EventType
  payload: EventPayload
}

interface WorkerChannelEventsMap {
  MOCK_RESPONSE: [
    data: StringifiedResponse,
    transfer?: [ReadableStream<Uint8Array>],
  ]
  PASSTHROUGH: []
}

export class WorkerChannel {
  constructor(private readonly port: MessagePort) {}

  public postMessage<Event extends keyof WorkerChannelEventsMap>(
    event: Event,
    ...rest: WorkerChannelEventsMap[Event]
  ): void {
    const [data, transfer] = rest
    this.port.postMessage({ type: event, data }, { transfer })
  }
}