I'm trying to create a variable to set one of the properties of an object obtained by the get method.

When I give console in subscribe I retrieve the value of the array, but I'm having difficulty (i'm beginner) to set only one of the properties of the objects in that array.

Component:

this.mainService.getGraph()
    .subscribe(res => {
      console.log(res) 
      this.name = res[''].map(res => res.name)
      console.log(this.name)

Console.log:

(5) […]
​
0: Object { name: "Carlos", lastname: "Moura", participation: 5 }
​
1: Object { name: "Fernanda", lastname: "Oliveira", participation: 15 }
​
2: Object { name: "Hugo", lastname: "Silva", participation: 20 }
​
3: Object { name: "Eliza", lastname: "Souza", participation: 20 }
​
4: Object { name: "Anderson", lastname: "Santos", participation: 40 }
​
length: 5
​
<prototype>: Array []
mainponent.ts:26:6
ERROR TypeError: "res[''] is undefined"
    ngOnInit mainponent.ts:27
    RxJS 13
    Angular 8

I'm trying to create a variable to set one of the properties of an object obtained by the get method.

When I give console in subscribe I retrieve the value of the array, but I'm having difficulty (i'm beginner) to set only one of the properties of the objects in that array.

Component:

this.mainService.getGraph()
    .subscribe(res => {
      console.log(res) 
      this.name = res[''].map(res => res.name)
      console.log(this.name)

Console.log:

(5) […]
​
0: Object { name: "Carlos", lastname: "Moura", participation: 5 }
​
1: Object { name: "Fernanda", lastname: "Oliveira", participation: 15 }
​
2: Object { name: "Hugo", lastname: "Silva", participation: 20 }
​
3: Object { name: "Eliza", lastname: "Souza", participation: 20 }
​
4: Object { name: "Anderson", lastname: "Santos", participation: 40 }
​
length: 5
​
<prototype>: Array []
main.ponent.ts:26:6
ERROR TypeError: "res[''] is undefined"
    ngOnInit main.ponent.ts:27
    RxJS 13
    Angular 8

• javascript
• angular
• typescript

Share Improve this question Follow asked Mar 4, 2019 at 15:49 Felipe NokaFelipe Noka 10733 silver badges99 bronze badges 4

• this.name = res[0].name;? <= assign the ponent's field name to the field name of the first object in the returned array. – Igor Commented Mar 4, 2019 at 15:52
• Can you be more specific about which property of user object you want to change / add? What value you want to give to "this.name" ? – Alexandre Nicolas Commented Mar 4, 2019 at 15:53
• what is the expected object structure? – Aravind Commented Mar 4, 2019 at 15:54
• i need to select all array names. because with these names I will create a doughnut chart with the results – Felipe Noka Commented Mar 4, 2019 at 16:00

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3 Answers 3

Sorted by: Reset to default 2

1. You are redefining res in your passed in function to map.
2. Use a plural of name to names, you want a string array so the plural is more appropriate and conveys what the field contains.
3. Do not try to access a non existent field or index on res, you had res[''] which is not correct.
4. I put the call in ngOnInit, it might be located elsewhere but this allowed me to define the assigned variable member above it.

names: string[];

ngOnInit() {
    this.mainService.getGraph()
      .subscribe(res => {
        console.log(res);
        this.names = res.map(_ => _.name);
        console.log(this.names);
}

---

From the ments:

...the IDE says property 'map' doesnt exist on type 'Object'. would it just be a bug

About your service. Make sure the signature is correct on the return type. Here is an example, you can also define an interface and return that instead of {name:string} (but keep the [] which denotes there is an array being returned).

import { HttpClient } from '@angular/mon/http';
import { Observable } from 'rxjs';

export class MainService {
  constructor(private readonly http: HttpClient){}

  getGraph() : Observable<{name: string}[]> {
    return this.http.get<{name: string}[]>('/some/url');
  }
}

Just use res.map(res => res.name). instead of res[''].map(res => res.name). In your case you are trying to access property with key equal to empty string inside of your object, and it doesn't exist

You can do it directly in the http get Method

this.http.get(url).pipe(
 map(res => {
   res['newProperty'] = 'value';
   return res;
 })
);

Even if you want just call back just one property

this.http.get(url).pipe(
     map(res => {       
       return res.name;
     })
    );