angular 5, how do I return an array from a promise?

Question

I am creating an array, after it is created that array is resolved as a Object. However as I need to sort tempArray based on a particular value after the resolve I need it as an array, not an Object. Also because after the sort I am displaying it using: *ngFor. Or is it better to somehow sort the Object instead of changing it back to an array?

The console.log of the returned Promise is displayed underneath.

var tempArray = []
return new Promise((resolve, reject) => {
  let error = false;
  var i = 0;
  for (let key of arrayOfPosts) {
    tempArray[i] = {
      "_id": key._id,
      "postPub": key.postPub,
      "timePast": this.timePastPublix
    }
    i++
  }

  if (error) {
    reject('error')
  } else {
    resolve(tempArray)
  }
});

{_id: "5aba1af4c97ce42ea81893bc", postPub: "0.00", timePast: "1970-01-01T01:00:00+01:00"}
{_id: "5ac698172910d705ecd66378", postPendingPayoutPublic: "0.00", timePast: "1970-01-01T01:00:00+01:00"}

Zze · Accepted Answer · 2018-04-07 23:58:46Z

7

You can just return it as an array, no need for an Object:

var promise = new Promise((resolve, reject) => {
  resolve([1,2,3,4,5]);
});

// reject example
var promise2 = new Promise((resolve, reject) => {
  var array = [];
  if(array.length == 0)
     reject("error");
  else
     resolve(array);
});

promise.then(data => console.log(data));
promise2.then(data => console.log(data))
        .catch(error => console.log(error));

Here is a stackblitz which uses the promise array return values in an *ngFor: https://stackblitz.com/edit/angular-vpkk1a

edited Apr 7, 2018 at 23:58

answered Apr 6, 2018 at 23:48

Zze

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4 Comments

Estus Flask Over a year ago

It's Promise.resolve(array). No need for promise construction function.

Zze Over a year ago

@estus You are correct, my example could be just that, however in the question it appears like they want some sort of error checking to take place within the promise.

oudekaas Over a year ago

When would we check for rejects, could you give an example? Your solution works.

Zze Over a year ago

@oudekaas Added an example which churns out an error.

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