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Hello

For what it's worth, I found using generators in Koa such a pleasure to get some easy to read and easy to maintain code .

Sample code (quickly edited to make it more generic rather than our real names, hopefully I haven't introduced any typos, the idea is to have a basic service that serve as a proxy to ElasticSearch, slightly modified here to only show the cascade of generators function* / yield)

In the server.ts file:

import {service1} from './controllers/service1/controllers';
router.get(`${config.routeService1}*`, service1.endpointService1);

In the controllers/service1/controllers.ts file, I define the generators

export namespace service1 {

    export function* endpointService1() {
    // Here I only digest the arguments and format the response , like a public-facing API for the module
        var args: IService1RequestArgs = {
            originalUrl: this.originalUrl,
            body: this.request.body,
            queryString: this.query
        };
        var myResponse: IService1RequestResult = yield forwardSearch(args);

        this.request.ctx.state.service1Logs = myResponse.logs; // the ctx.state is consumed by middleware added to the server for logs, formatting, profiling, ...
        this.body = myResponse.body;
    }

    export function* forwardSearch(searchArgs: IService1RequestArgs) {

        // Read the search query
        const searchString: string = searchArgs.queryString.q;

        const localRoute = `${config.routePrefix}${config.routeSearch}`;
        const targetUrl: string = searchArgs.originalUrl.replace(localRoute, '');

        // Send this to  Elasticsearch
        const options = {
            headers: {
                'User-Agent': `${config.userAgent}`,
                'Authorization': `${config.esAuth}`
            },
            url: `${config.esSearchEndpoint}${targetUrl}`,
            method: 'POST',
            qs: searchArgs.queryString,
            json: true,
            body: searchArgs.body
        };

        // And forward the response
        const kresponse = yield krequest(options);

        const results: IESResponse = <IESResponse>kresponse.body;

        // If the response is valid, read some info to report the results
        const logs: ISearchLog = myLogger.getBasicLogProps();
            // Here add other properties about what you want to debug/profile/log, ...

        return {
            body: results,
            logs: logs
        };
    }
}

In other services, one request triggers a cascade of calls (get result from a service A, then send a result from A to B, and send back a response composed from the combination of A and B. Using generators and yield makes it very easy to read and handle.