Can you explain the functionality of this Observable in the context of this Angular 2 example?

I'm not too familiar with JavaScript/TypeScript and I have a question about how this code snippet works:

  onGet() {
    this.serverService.getServers()
      .subscribe(
        (servers: any[]) => this.servers = servers,   // an array of anything (or an array of server)
        (error) => console.log(error)
      );
  }

As far as I understand, the onGet() method is calling the getServers() method which returns an **Observable, and then it subscribes to this returned Observable object.

My understanding of Observables is that they represent a stream of data where you can perform actions based on events. However, I'm uncertain about the specific functionality of this part of the code:

    (servers: any[]) => this.servers = servers,   // an array of anything (or an array of server)
    (error) => console.log(error)

Could someone explain how this part works?

javascriptangulartypescriptjavascript-frameworkangular2-observables

Answer №1

(serverList: any[]) => this.serverList = serverList,   // storing an array of servers
(error) => console.log(error)

can be written as 

(serverList: any[]) => { //handling success case
       this.serverList = serverList;   // storing an array of servers
},
(error) => { //handling error case
        console.log(error);
}

The first function serves as the success callback and the second one acts as the error callback which are triggered based on the outcome of the getServers() method.

Answer №2

   // the following function will handle responses that are not errors
   (servers: any[]) => this.servers = servers,
   // if there is an error response, whether it be a http error or thrown error
   (error) => console.log(error)

It seems like the serverService call is fetching a list of servers and populating this.servers with that data. In case of any errors, such as 4XX or 5XX errors, they will be logged to the console. The observable will always be resolved and closed regardless of success or failure. If you need an observable that can be updated dynamically over time, consider using a Subject.

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