worker-factory/src/helpers/create-message-handler.ts

A little factory function to create a JSON-RPC based Web Worker implementation.

import { IBrokerEvent, IErrorNotification, IErrorResponse, IReceiver, IRequest, IWorkerDefinition } from '../interfaces';
import { TMessageReceiverWithParams, TMessageReceiverWithoutParams, TWorkerImplementation } from '../types';
import { renderMethodNotFoundError, renderMissingResponseError, renderUnexpectedResultError } from './error-renderers';

export const createMessageHandler = <WorkerDefinition extends IWorkerDefinition>(
    receiver: IReceiver,
    workerImplementation: TWorkerImplementation<WorkerDefinition>
) => {
    return async ({ data: { id, method, params } }: IBrokerEvent<WorkerDefinition>) => {
        const messageHandler = workerImplementation[method];

        try {
            if (messageHandler === undefined) {
                throw renderMethodNotFoundError(method);
            }

            const response =
                params === undefined
                    ? (messageHandler as TMessageReceiverWithoutParams<WorkerDefinition[typeof method]['response']>)()
                    : (
                          messageHandler as TMessageReceiverWithParams<
                              WorkerDefinition[typeof method]['params'],
                              WorkerDefinition[typeof method]['response']
                          >
                      )(params);

            if (response === undefined) {
                throw renderMissingResponseError(method);
            }

            const synchronousResponse = response instanceof Promise ? await response : response;

            if (id === null) {
                if (synchronousResponse.result !== undefined) {
                    throw renderUnexpectedResultError(method);
                }
            } else {
                if (synchronousResponse.result === undefined) {
                    throw renderUnexpectedResultError(method);
                }

                const { result, transferables = [] } = <IRequest['response']>synchronousResponse;

                receiver.postMessage({ id, result }, transferables);
            }
        } catch (err) {
            const { message, status = -32603 } = err;

            receiver.postMessage(<IErrorNotification | IErrorResponse>{ error: { code: status, message }, id });
        }
    };
};