CODEWITHSUNDEEP
javascriptecmascript-6promisees6-promise
shinzou
shinzou

Reputation: 6232

Reject a promise from then()

How can you reject a promise from inside its then()?

For example:

Promise.all(promiseArr).then(()=>{
  if(cond){
    //reject
  }
}).catch(()=>{ /*do something*/ });

The only relevant question I found was this: How to reject a promise from inside then function but it's from 2014, so there must be a better way then to throw by now with support of ES6.

Upvotes: 11

Views: 9083

Answers (2)

Pete
Pete

Reputation: 61

I have found out (after hours of scratching my head) that if a throw is within an async method such as setTimeout(() => throw new Error('description')) it will be treated as an Unhandled Exception and will NOT end up in your .catch() block (you'll only see it in the console window) - see this article where I found out about that difference between throw and Promise.reject.

Upvotes: 2

Estus Flask
Estus Flask

Reputation: 223044

ES6/ES2015 is still JavaScript and doesn't offer anything new regarding promise rejection. In fact, native promises are ES6.

It is either

promise
.then(() => {
  return Promise.reject(...);
})
.catch(...);

or

promise
.then(() => {
  throw ...;
})
.catch(...);

And throw is more idiomatic (and generally more performant) way to do this.

This may not be true for other promise implementations. E.g. in AngularJS throw and $q.reject() is not the same thing.

Upvotes: 11

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