worker-facade

Message-passing TypeScript utilities for Worker

worker-facade is a TypeScript library of utilities designed to simplify message-based interaction with Worker instances, as well as their implementation:

• The WorkerFacade interface includes only a subset of Worker's methods: the ones for message passing, from the perspective of clients

• The RequestListener function type turns the implementation of a worker into a one-liner, while enabling the creation of mocks (already implementing the WorkerFacade interface) via the worker-mock library

Installation

The package on NPM is:

@giancosta86/worker-facade

The public API entirely resides in the root package index, so one shouldn't reference specific modules.

Usage

The practical aspects of this library can be summarized as follows:

• when you need to interact with a Worker via messages, pass its clients the WorkerFacade interface instead of the Worker itself - because:

  • WorkerFacade is structurally supported by Worker, but provides less methods

  • in tests, you can mock the worker by instantiating a WorkerMock - provided by the worker-mock package

• declare the body of your worker as a function compatible with the RequestListener function type - that is, taking these parameters:

  • the request itself

  • a sendResponse(response) function - that can be called as many times as required, to send response messages

  This way:

  • in the worker script, just call RequestListener.register(self, <your listener function>) - without having to take care of message events

  • when mocking the worker, especially in tests, just call WorkerMock.create(<your listener function>) to have a full-fledged mock

API documentation

WorkerFacade

WorkerFacade<TRequest=unknown> is an interface providing just the methods required to perform message passing with any kind of Worker instance:

• postMessage() - sending a request message, of type TRequest, to the worker interface; you must pass the message itself, which will be wrapped into a dedicated event.

• addEventListener() - only supporting the message, messageerror and error events - expressed by the WorkerFacade.EventType union type; listeners are called when the worker responds

• removeEventListener() - used to remove a listener for one of the supported event types

WorkerFacade is a subset of Worker's interface - and it is also explicitly implemented by WorkerMock, in the worker-mock package.

WorkerFacade.EventType

Union type defining the only events supported by this message-passing facade:

• message

• messageerror

• error

WorkerFacade.EventListener

Should you need to store message-related event listeners into callback variables, you can use the WorkerFacade.EventListener function type - which is focused on the events supported by WorkerFacade.

RequestListener

RequestListener<TRequest, TResponse> is a type describing a function with 2 arguments:

• a request, of type TRequest - the actual data (not the event) that must be processed

• a ResponseSender - actually, a function whose first parameter is a response to be sent to the client

RequestListener is an abstraction used to:

• simplify the actual implementation of a Worker

• enable the creation of a mock, in the worker-mock package

Further references

• worker-mock - Minimalist Worker mocks in TypeScript