CODEWITHSUNDEEP
javascriptangular
etayluz
etayluz

Reputation: 16436

Passing params to mapped observable

I'm fairly new to Observables, Promises, Angular 2, and Javascript.

My question is how do I get a reference to the "item" object here:

  getItemTransactions (item: Item): Observable<any> {
    // Do some stuff ...

    return this.http.post(this.url, body, options)
                    .map(this.extractData)
                    .catch(this.handleError);
  }

In the mapped extractData helper?

  private extractData(res: Response) {
    let json = res.json().body

    /// How do I assign back to item object here?
    item.some_property = json["some_property"]
  }

Code come from here: https://angular.io/docs/ts/latest/guide/server-communication.html#!#extract-data

Upvotes: 0

Views: 259

Answers (2)

Igor
Igor

Reputation: 62238

  1. Map should be used to convert a type to another type. When using the http service you should convert your expected json result to some expected and known type. This can be done using .json() method on the response.
  2. Use subscribe to then do something with the expected result from .json().

All of your actions can be done in the expression body, you do not need separate methods for them. This is a mater of preference so whatever you choose is fine.

See code below.

getItemTransactions (item: Item): Observable<any> {
// Do some stuff ...

  return this.http.post(this.url, body, options)
                .map((res) => res.json()) // get the data from the json result. This is equivalent to writing {return res.json()}
                .subscribe((data) => {
                  this.doSomethingWithData(data, item); // pass that deserialized json result to something or do something with it in your expression
                })
                .catch(this.handleError);
}

private doSomethingWithData(data: any, item: Item) {
  // Do some stuff ...

  item.some_property = data["some_property"];
}

Upvotes: 1

AngularChef
AngularChef

Reputation: 14087

Why would you want to re-assign a method parameter in the first place? You probably want to assign a class property instead (this.item vs item).

But if for some reason you really want to reassign the item param, you could always inline the extractData helper, i.e.:

getItemTransactions(item: Item): Observable<any> {
  return this.http.post(this.url, body, options)
                .map((res: Response) => {
                  item = res.json();  // Re-assign some value to `item`
                })
                .catch(this.handleError);
}

It's probably NOT what you want to do. The usual pattern is to have a function return an observable and subscribe() to that observable somewhere else in your code. You can do the assignment inside the subscribe callback.

This would translate to the following code:

getItemTransactions(item: Item): Observable<any> {
  return this.http.post(this.url, body, options)
                .map((res: Response) => res.json())
                .catch(this.handleError);
}

// Somewhere else in your code
this.getItemTransactions(item: Item).subscribe(data => {
  item = data; // for instance
}

Upvotes: 1

Related Questions