CODEWITHSUNDEEP
javascriptecmascript-6breakchain
Eduard Bondarenko
Eduard Bondarenko

Reputation: 363

What is the good way to break from promise chain?

I am wondering how can I properly break promise chain in JS.

In this code, I am connecting to database at first, then I am checking if collection already has some data, if not add them. Don't pay attention to some actionhero.js code..it does not matter here.

The main question is: Is it okay to break chain using throw null?

mongoose.connect(api.config.mongo.connectionURL, {})
        .then(() => {
            return api.mongo.City.count();
        })
        .then(count => {
            if (count !== 0) {
                console.log(`Amout of cities is ${count}`);
                throw null; // break from chain method. Is it okay ?
            }
            return api.mongo.City.addCities(api.config.mongo.dataPath + '/cities.json');
        })
        .then(cities => {
            console.log("Cities has been added");
            console.log(cities);
            next();
        })
        .catch(err => {
            next(err);
        })

Many thanks!

Upvotes: 0

Views: 74

Answers (1)

Роман Парадеев
Роман Парадеев

Reputation: 4266

Despite it may seem like a clever trick and will work as You expect, I would advise against throwing non-error objects.

It would be much more predictable for other developers that will maintain this code if You throw an actual Error and handle it explicitly.

Promise
  .resolve()
  .then(() => {
    throw new Error('Already in database');
  })
  .catch(err => {
    if (err.message === 'Already in database') {
      // do nothing
    } else {
      next(err);
    }
  });

Upvotes: 2

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