CODEWITHSUNDEEP
javascripttypescriptpromisebluebird
rubenhak
rubenhak

Reputation: 890

Intentionally not returning Bluebird Promise

I have the piece of code below. Want to call the callback which may return a promise. Resolve it. In case if the promise failed, log it. The caller should NOT know about all this and should return without waiting for the promise to fulfill. That's why I'm not returning the promise. This causes the following error:

(node:21146) Warning: a promise was created in a handler at internal/timers.js:456:21 but was not returned from it, see http  goo.gl/rRqMUw
    at Function.Promise.cast (bluebird/js/release/promise.js:225:13)

I've read the docs and they recommend returning null to prevent the warning from happening. Nevertheless, the warning still pops out. Also, do not want to disable the warning globally.

    private _trigger(cb : () => Resolvable<any>)
    {
        try
        {
            const res = cb();
            const prom = Promise.resolve(res);
            prom.catch(reason => {
                this.logger.error("ERROR: ", reason);
            })
        }
        catch(reason)
        {
            this.logger.error("ERROR: ", reason);
        }
        return null;
    }

Upvotes: 2

Views: 122

Answers (1)

CertainPerformance
CertainPerformance

Reputation: 370889

The internal Promise should resolve to a value of null to silence the warning - this will tell Bluebird "The Promise isn't being returned, but since it resolves to null, it doesn't contain a useful result, so this is deliberate"; returning it wouldn't give the caller useful data. You can do something like:

const prom = Promise.resolve(res)
  .catch(reason => {
    this.logger.error("ERROR: ", reason);
  })
  .then(() => null);

Upvotes: 1

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