Making polling request in Angular 2 using Observable

Question

I have the following code to make a polling GET request in AngularJS 2:

 makeHtpGetRequest(){
            let url ="http://bento/supervisor/info";
            return Observable.interval(2000)
                .map(res => res.json()) //Error here
                .switchMap(() => this.http.get(url));

            /*
    This portion works well
    return this.http.get(url)
                .map(res =>res.json());*/
        }

TypeScript is giving me an error make the response in JSON format (check comment in the code.

TypeError: res.json is not a function

Surprisingly, it was working for some time and I am not sure if I changed anything else, but it stopped working.

The commented part in the code works very well.

Mark Rajcok · Accepted Answer · 2016-02-24 04:24:34Z

12

Try

return Observable.interval(2000) 
        .switchMap(() => this.http.get(url))
        .map(res:Response => res.json());

answered Feb 24, 2016 at 4:24

Mark Rajcok

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1 Comment

kosta Over a year ago

I tried this. It still gives me the error. However, it does the polling in any case.

Pradeep · Accepted Answer · 2016-09-26 14:26:31Z

5

It might be too late, but it might still help someone.

According to doc

This is not Angular's own design. The Angular HTTP client follows the ES2015 specification for the response object returned by the Fetch function. That spec defines a json() method that parses the response body into a JavaScript object.

I think json function only exists in http's response

I would try

return Observable.interval(2000) 
        .switchMap(() => this.http.get(url).map(res:Response => res.json()));

edited Sep 26, 2016 at 14:26

Pradeep

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answered Jun 28, 2016 at 15:39

maxisam

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Comments

Emile Cantero · Accepted Answer · 2017-05-11 09:26:00Z

2

What you could do is, don't forget to cleanup you setInveral otherwise it will run forever :

let myObservable = new Observable(observer => {
     let count = 0;
     let interval = setInterval(() => {
           observer.next(count++);
  },2000);

 //disposal function
return() => {
   clearInterval(interval);
 }
});


let subscriber = myObservable.subscribe(
  val => console.log(val),
  err => console.log(err),
  _ => console.log('done')
);

subscriber.unsubscribe();

answered May 11, 2017 at 9:26

Emile Cantero

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