RxJS: http requests on delay

Question

I am just migrating one of my applications to Angular 2 and with it comes RxJS.

I want to refresh my data from server every 5s. At first I figured to do something like this:

Observable.timer(0,5000).flatMap(() => this.http.get(url))

But if the http request takes more than 5 seconds, another one gets sent. I would like it to wait 5s after http request is finished not after it is created.

cyr_x · Accepted Answer · 2017-03-21 10:07:44Z

4

You can use the expand Operator to create a new Observable when the source emits an item.

let myRequest = this.http.get(...);
let pollingSubscription = myRequest
 .expand(() => Observable.timer(5000).flatMap(() => myRequest));
 .subscribe();

Docs for expand

Litte bit offtopic but maybe you should look into something like LongPolling

answered Mar 21, 2017 at 10:07

cyr_x

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2 Comments

Luka Over a year ago

This sounds perfect, will try it in today. As for websockets, unfortunately we are working with a fixed backend.

cyr_x Over a year ago

LongPolling have nothing to do with Websockets ;)

Pardeep Jain · Accepted Answer · 2017-03-21 10:08:17Z

1

One approach you can adopt is

RequestGet(){
     this.http.get(url)
          .subscribe(e=>{
              // check if response get or not properly
              // if yes call another method
              this.againRequest();
          })
  }
  againRequest(){
    setTimeout(e => {
      this.RequestGet()
    }, 5000)
  }

answered Mar 21, 2017 at 10:08

Pardeep Jain

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