returning instance of a pom client in a function and accessing it from another file lose context

Question

I have a typescript class as follows:

const client = require('prom-client');


export default class Monitoring {

  // public client: any;
  private _logger: LoggingService;

  public constructor(logger: LoggingService) {
    // this._pomClient = client;
    this._logger = logger;
  }

  public async executePromClient() {
    this._logger.debug({message: `Returning prom client isnatnce`})
    const histogram = new client.Histogram({
      name: 'http_request_duration_seconds1',
      help: 'Duration of HTTP requests in seconds histogram',
      labelNames: ['method', 'handler', 'code'],
      buckets: [0.1, 5, 15, 50, 100, 500],
    });
    return histogram;
  }

  public async getPromClient() {
    this._logger.debug({message: `Returning prom client isnatnce`})
    return  client;

  }

he execute function works fine and not a problem however when I call getPromClient() in my server ts as follows:

const monitoring = new Monitoring(
  loggingService,
);
// const client = require('prom-client');
const client: any = monitoring.getPromClient();
// enable prom-client to expose default application metrics
const collectDefaultMetrics = client.collectDefaultMetrics;

I get

TypeError: collectDefaultMetrics is not a function
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Module.require (internal/modules/cjs/loader.js:952:19)

I am so confused I am just returning the client and trying to use in in sercer.ts why is it not working?

Answer 1

You declared getPromClient() as async. That means it would return a Promise if you don't await it. As you didn't await anything within getPromClient(), simply remove the async will solve the problem.

public getPromClient() {
    this._logger.debug({message: `Returning prom client isnatnce`})
    return  client;
}

You probably don't know what async mean and just declaring it everywhere which you shouldn't. You can learn more about it here