What is the best way to allocate inner JSON to an object within a promise?

Exploring the Angular2 tutorial "Tour of Heroes" showcases how to handle JSON data within a promise. But what if the JSON structure is more complex?

JSON:

let complexMessage = [{
      "heroes":[
      {id: 11, name: 'Mr. Nice'},
      {id: 12, name: 'Narco'},
      {id: 13, name: 'Bombasto'},
      {id: 14, name: 'Celeritas'},
      {id: 15, name: 'Magneta'},
      {id: 16, name: 'RubberMan'},
      {id: 17, name: 'Dynama'},
      {id: 18, name: 'Dr IQ'},
      {id: 19, name: 'Magma'},
      {id: 20, name: 'Tornado'}
      ]
      ,"numHeroes": 9
      ,"messages":[
        {message: "aaa", args:[]},
        {message: "bbb", args:[]}
      ]
    }];

The provided Typescript snippet encounters issues with handling multidimensional JSON:

getHeroes(): Promise<Hero[]> {
    return this.http.get(this.heroesUrl)
               .toPromise()
               .then(response => response.json())
               .catch(this.handleError);

Then we see:

getHeroes() {
    this.heroService
        .getHeroes()
        .then(heroes => this.heroes = heroes)
        .catch(error => this.error = error);
  }

Is there a way to extract and assign the inner "heroes" array to this.heroes in the code above? (The original tutorial can be found at https://angular.io/docs/ts/latest/tutorial/toh-pt6.html)

Answer №1

For extracting the heroes data from this JSON file specifically, you can achieve it with the following code snippet:

fetchHeroes(): Promise<Hero[]> {
    return this.http.get(this.heroesUrl)
               .toPromise()
               .then(response => response.json()[0].heroes)
               .catch(this.handleError);

Answer №2

To achieve the desired outcome, simply assign the "heroes" array instead of the full response to "this.heroes". Alternatively, you can also specify the desired array during the http call. Here's an example:

getHeroes(): Promise<Hero[]> {
    return this.http.get(this.heroesUrl)
               .toPromise()
               .then(response => response.json())
               .catch(this.handleError);

getHeroes() {
    this.heroService
        .getHeroes()
        .then(heroes => this.heroes = heroes[0].heroes) // Retrieve the first key from the array to get the heroes data
        .catch(error => this.error = error); 
  }

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