CODEWITHSUNDEEP
angularionic-frameworkrxjsobservableionic4
wiseindy
wiseindy

Reputation: 19655

How do I subscribe to an Observable and use that value in a Javascript Object?

I'm fairly new to Observables, RxJS and Angular in general. I'm using Angular 7 (Ionic 4) and am having a hard time wrapping my head around a solution to the problem below.

In my application, I make an HTTP GET request as follows:

myData = this.http.get("https://example.com/api").pipe(
  map(results => {
    return results["payload"]
  })
)

This HTTP GET request returns an Observable myData which has the following data:

const data = [
  {
    "id": 1,
    "name": "abc",
    "description": "test1" 
  },
  {
    "id": 2,
    "name": "def",
    "description": "test2" 
  },

  ...

  ...

]

I want to add another key color to each object in this array like this:

const data = [
  {
    "id": 1,
    "name": "abc",
    "description": "test1",
    "color": "green"
  },
  {
    "id": 2,
    "name": "def",
    "description": "test2",
    "color": "red"
  },

  ...

  ...

]

Instead of hard coding the value of color for each object, I want to retrieve this key value from a function getColor(id) which is in another service called colorService.

The problem is that that colorService.getColor(id) returns an Observable.

The question: How can I subscribe to colorService.getColor(id) for each object in my array?

I want to do something like this:

const data = [
  {
    "id": 1,
    "name": "abc",
    "description": "test1",
    "color": <subscribe to colorService.getColor(1)>
  },
  {
    "id": 2,
    "name": "def",
    "description": "test2",
    "color": <subscribe to colorService.getColor(2)>
  },

  ...

  ...

}

I hope I'm clear. My concepts are rather weak at this point, so apologizes if some of it sounds confusing.

Upvotes: 1

Views: 258

Answers (1)

user2216584
user2216584

Reputation: 5612

This is what you can do [See the explanation in the code comments]- 

myData = this.http.get("https://example.com/api")
                      .pipe(
                              mergeMap(results => {
                                const data = results["payload"];
                                //I am assuming that `data` is the array that you mentioned in your question
                                //Iterate through each of the object in the array and map it to an observable which
                                //will fetch the color and then return the data with color

                                //obs will be an array of observables for each data
                                const obs = data.map(d => {                                  
                                  return this.colorService.getColor(d.id)
                                             .pipe(
                                               map(color => {
                                                 return {...d, color};
                                               })
                                             );
                                });

                                //wait for all the obs to be returned;
                                return forkJoin(obs);
                              }),
                              tap(dataArrayWithColor => {
                                //dataArrayWithColor will have an array of object which will have data with color
                                console.log(dataArrayWithColor);
                              })
                          );

Hope it helps.

Upvotes: 2

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